943 Ergebnisse für: "AbFrontier"

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ERK1 and ERK2 are widely expressed and are involved in the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells.
Many different stimuli, including growth factors, cytokines, virus infection, ligands for heterotrimeric guanine nucleotidebinding protein (G protein)-coupled receptors and transforming agents, activate the ERK1 and ERK2 pathways. When growth factors bind to the receptor tyrosine kinase, Ras interacts with Raf, the serine/threonine protein kinase and activates it as well. Once actived, Raf phosphorylates serine residue in 2 further kinases, MEK1/2, which in turn phosphorylates tyrosine/threonine in extracellular-signal regulated kinase(ERK) 1/2. Upon activation, the ERKs either phosphorylate a number of cytoplasmic targets or migrate to the nucleus, where they phosphorylate and activate a number of transcription factors such as c-Fos and Elk-1.

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Anti-Peroxiredoxin 5 Rabbit Polyclonal Antibody

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The complement system is a part of the larger immune system and three biochemical pathways are present: the classical complement pathway, the alternative pathway, and the mannose-binding lectin pathway.
Complement component C4 is an essential component of humoral immune response. In its activated form, C4b becomes a subunit of the C3 convertase, which is an enzymatic complex that activates C3 of the classical and lectin complement activation pathways. The classical pathway is initiated by the activation of the C1-complex (C1q, C1r and C1s) by C1q's binding to antibody-antigen. The C1-complex now binds to and splits C2 and C4 producing C2a and C4b. C4b and C2a bind to form C3-convertase. Production of C3-convertase leads to cleavage of C3 into C3a and C3b and C3b joins with the C3 convertase to make C5 convertase.
Human C4 is the most polymorphic protein of the complement system. Complement C4 exists as two isotypes, C4A (acidic) and C4B (basic). Although the sequence identity is very high, they have different hemolytic activities, covalent affinities to antigens and immune complexes, and serological reactivities. Each C4 contains β chain, α chain, C4a anaphyltoxin, C4b, and γ chain.
C4-deficient mice shows incomplete clearance of microbial attack and C4-deficiency in human shows increased autoimmune diseases.

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PTEN acts as a phosphatase to dephosphorylate phosphatidylinositol (3,4,5)-trisphosphate (PtdIns (3,4,5)P3). The product of this enzymatic reaction is PtdIns(4,5)P2. This dephosphorylation is important because it results in inhibition of the AKT signaling pathway.
PTEN is a 403 amino acid protein, and a member of the large PTP (protein tyrosine phosphatase) family. PTEN crystal structure revealed that the N-terminal phosphatase domain is followed by a tightly associated C-terminal C2 domain. These two domains together form a minimal catalytic unit. The phosphatase domain contains the active site which carries out the enzymatic function of the protein, whilst the C2 domain allows PTEN to bind to the phospholipid membrane.
PTEN is one of the most commonly lost tumour suppressors in human cancer, and its deregulation is also implicated in several other diseases. Hereditary mutation of PTEN causes tumor-susceptibility diseases such as Cowden disease.

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Mammalian target of rapamycin (mTOR), a serine/threonine kinase involved in diverse cellular processes, including protein translation, mRNA turnover, and protein stability, mediates, at least in part, some of the biological actions of Akt. As a Kinase subunit of both mTORC1(complex1) and mTORC2(complex2), mTOR regulates cell growth and survival in response to nutrient and hormonal signals. mTORC1 is activated in response to growth factors or amino-acids. Activated mTORC1 up-regulates protein synthesis by phosphorylating key regulators of mRNA translation and ribosome synthesis. mTORC1 phosphorylates EIF4EBP1 and releases it from inhibiting the elongation initiation factor 4E (eiF4E). mTORC2 seems to function upstream of Rho GTPases to regulate the actin cytoskeleton, probably by activating one or more Rho-type guanine nucleotide exchange factors. mTORC2 promotes the serum-induced formation of stress-fibers or F-actin. mTORC2 plays a critical role in AKT1 'Ser-473' phosphorylation.

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Anti-PTPRM Mouse Monoclonal Antibody [clone: T5-AF1A8]

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Dual specificity phosphatase 13(Also known as BEDP; MDSP; TMDP; SKRP4; DUSP13A; DUSP13B) is an enzyme that in humans is encoded by the DUSP13 gene.[1]
Members of the protein tyrosine phosphatase superfamily cooperate with protein kinases to regulate cell proliferation and differentiation. This superfamily is separated into two families based on the substrate that is dephosphorylated. One family, the dual specificity phosphatases (DSPs) acts on both phosphotyrosine and phosphoserine/threonine residues. This gene encodes different but related DSP proteins through the use of non-overlapping open reading frames, alternate splicing, and presumed different transcription promoters. Expression of the distinct proteins from this gene has been found to be tissue specific and the proteins may be involved in postnatal development of specific tissues. A protein encoded by the upstream ORF was found in skeletal muscle, whereas the encoded protein from the downstream ORF was found only in testis. In mouse, a similar pattern of expression was found. Multiple alternatively spliced transcript variants were described, but the full-length sequence of only some were determined.[1]

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Peroxiredoxin (Prx) is a growing peroxidase family, whose mammalian members have been known to connect with cell proliferation, differentiation, and apoptosis.
Many isoforms (about 50 proteins), collected in accordance to the amino acid sequence homology, particularly amino-terminal region containing active site cysteine residue, and the thiol-specific antioxidant activity, distribute throughout all the kingdoms. Among them, mammalian Prx consists of 6 different members grouped into typical 2-Cys, atypical 2-Cys Prx, and 1-Cys Prx. Except Prx VI belonging to 1-Cys Prx subgroup, the other five 2-Cys Prx isotypes have the thioredoxin-dependent peroxidase (TPx) activity utilizing thioredoxin, thioredoxin reductase, and NADPH as a reducing system. Mammalian Prxs are 20 – 30 kilodalton in molecular size and vary in subcellular localization: Prx I, II, and VI in cytosol, Prx III in mitochondria, Prx IV in ER and secretion, Prx V showing complicated distribution including peroxisome, mitochondria and cytosol (1).

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STAT2 (Signal transducer and activator of transcription 2), 113kDa, is a member of the STAT family of cytoplasmic transcription factors. STAT members generally mediate cytokine, growth factor and hormone receptor signal transduction. STAT2 is a transcription factor critical to the signal transduction pathway of type I interferons (e.g. IFNα). STAT2 resides primarily in the cytoplasm and is tyrosine-phosphorylated after IFNα binds to cell surface receptors. In response to tyrosine phosphorylation STAT2 rapidly localizes to the nucleus and acquires the ability to bind specific DNA targets in association with two other proteins, STAT1 and IFN regulatory factor-9 (IRF-9). STAT2 is phosphorylated at Y689 by receptor-associated Janus kinasses (JAKs) leading to STAT2 dimerization and subsequent translocation to the nucleus to activate gene transcription.

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The RIP(receptor-interacting protein) family of serine/Threonine kinases(RIP-1,2,3,4,5,6,7) are crucial regulators of cell survival and cell death that can trigger pro-survival, inflammatory and immune responses via the activation of transcription factors(NF-kB and AP-1) and death-inducing programs.
RIP2(also known as RICK, CARDIAK, CCK and Ripk2) transduces signals from receptors of both immune responses. RIP2 carries a CARD at its C-terminal, which is essential for NF-kB activation. RIP2 is a critical downstream mediator of Nod1 and Nod2 signaling. Overexpression of RIP2 results in the activation of, in addition to NF-kB, the MAPKs JNK and ERK2, requiring its kinase activity to activate ERK2, but not JNK.

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Focal adhesion kinase subfamily consists of the non-receptor proline-rich protein tyrosine kinases (PTKs). Two members of the family are focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (PYK2). These two kinases have molecular mass between 110-125 kDa and are closely related in their structure. The presence of two proline-rich motifs within the C-terminal domains is conserved.
FAK is a nonreceptor and nonmembrane associated PTK which does not contain Src homology 2 (SH2) or SH3 protein interaction domains. The centrally located kinase domain of FAK is flanked by large N- and C-terminal noncatalytic domains.
FAK links integrin receptors to intracellular signaling pathways that are important for cell growth, survival, and migration. Integrin receptor engagement with ligands such as fibronectin can stimulate FAK autophosphorylation which enables FAK to function within a network of integrin-stimulated signaling pathways leading to the activation of targets such as the ERK and JNK/mitogen-activated protein kinase pathways. Recent study reveals that FAK is essential for angiogenesis in the embryo, functions in heart development and modulates the response of cardiomyocytes to pressure overload in adult mice.

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Vimentin is a member of the intermediate filament family of proteins found in various non-epithelial cells, especially mesenchymal cells. Vimentin is responsible for maintaining cell shape, integrity of the cytoplasm, and stabilizing cytoskeletal interactions. Vimentin plays a significant role in supporting and anchoring the position of the organelles in the cytosol. Although most intermediate filaments are stable structures, vimentin also has a dynamic nature which is important when offering flexibility to the cell.
Two monomers which have central α-helical domains, capped on each end by non-helical domains twist around each other to form a coiled-coil dimer. Two dimers then form a tetramer, which, in turn, form a sheet by interacting with other tetramers.
There are some reports related to the biochemical function of intermediate filament network. The intracellular movement of LDL-derived cholesterol from the lysosome to the site of esterification is a vimentin-dependent process. A role for vimentin in mechanotransduction of shear stress has also been suggested. The mechanical stress of fluid shear on endothelial cells seems to trigger MAPK signaling pathways and stimulates proliferation.

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Heat shock proteins are ubiquitous proteins and have been characterized as cytoprotective molecular chaperones. The typical function of a chaperone is to assist a protein to attain its functional conformation to prevent non-functional aggregation of misfolded proteins. The principal HSP families are HSP90, HSP70, HSP60 and the small HSPs including HSP27, ubiquitin, α-crystallin, Hsp20 and others. The common functions of small Hsps are chaperone activity, thermotolerance, inhibition of apoptosis, regulation of cell development, and cell differentiation.
Hsp27 has a molecular weight of approximately 27 kDa, although it has been shown to form large aggregates of up to 800 kDa in the cytosol. Hsp27 is found in several types of human cells, including tumour cells. Hsp27 interferes with apoptosis through its ability to interact with and inhibit key components of the apoptotic signaling pathway, including the caspase activation complex. Overexpression of heat shock proteins can increase the tumorigenic potential of tumour cells. HSP27 also has been reported to be involved in development and progression of hormone-refractory prostate cancer.

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Platelet-derived growth factors (PDGFs) have been implicated in the control of cell proliferation, survival and migration. The PDGF family of growth factors consists of five different disulphide-linked dimers built up of four different polypeptide chains encoded by four different genes. Theses isoforms, PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, act via two receptor tyrosine kinases, PDGF receptors α and β. Thus far, gene-targeting experiments have been attempted to create knockout mice deficient for PDGFR-α or PDGFR-β. Those mice, however, died either at the embryonic stage or several days after birth. Platelet-derived growth factor receptors, PDGFR-α and PDGFR-β, have five extracellular immunoglobulin-like domains and an intracellular tyrosine kinase domain. Upon binding a PDGF, the receptors form homo- and heterodimers. Dimerization of the receptors juxtaposes the intracellular part of the receptors, which allow phosphorylation in trans between the two receptors in the complex. These autophosphorylation provide docking sites for downstream signal transduction molecules. More than 10 different SH2–domain-containing molecules have been shown to bind to different autophosphorylation sites in the PDGF α- and β-receptors. There are signal transduction molecules with enzymatic activity, such as PI3-kinase, PLC-γ, Src, SHP-2, GAP, as well as adaptor molecules such as Grb2, Shc, Nck, Grb7 and Crk, and Stats. Each of the different partners recruited by the activated receptor initiates different signaling pathways, making possible a great variety of cellular response.

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Amphiphysins, members of the BAR (Bin-Amphiphysin-Rvsp) protein super family, play a key role in clathrin-mediated endocytosis of synaptic vesicles (SVs). All members of the BAR family share a highly conserved N-terminal BAR domain and a C-terminal Src homology (SH3) domain. Two isoforms of amphiphysin have been identified and act in concert as a heterodimer. Amphiphysins interact via its carboxy-terminal SH3 domain with dynamin, synaptojanin and clathrin. These complexes are implicated in synaptic vesicle recycling at nerve terminal.  Amphiphysins were also identified as the dominant autoantigen in paraneoplastic Stiff-Man Syndrome.

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Ataxia telangiectasia mutated (ATM) is a serine/threonine-specific protein kinase that is activated by DNA double-strand breaks. It phosphorylates several key proteins that initiate activation of the DNA damage checkpoint, leading to cell cycle arrest, DNA repair or apoptosis. Several of these targets are p53, CHK2, BRCA1, and H2AX.
ATM triggers the G1/S checkpoint; ATR (Ataxia telangiectasia and Rad3-related) prevents G1/S stasis. In this single point in the cell cycle, it would appear that ATM and ATR function in opposition to one another.
Ataxia telangiectasia (AT) is a rare neurodegenerative, autosomal recessive disorder characterized by chromosome instability, radiosensitivity, immunodeficiency and a predisposition for cancer.
The ATR (ATM and Rad3-related) kinase and its downstream effector kinase, Chk1, are central regulators of the replication checkpoint. Loss of these checkpoint proteins causes replication fork collapse and chromosomal rearrangements. ATR are thought to be master controllers of cell cycle checkpoint signaling pathways that are required for cell response to DNA damage and for genome stability.

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Fibronectin (FN) exists in two main forms: 1) as a soluble glycoprotein in blood plasma (plasma FN), and 2) as an insoluble glycoprotein in tissue extracellular matrices (cellular FN). Many different cell types synthesize fibronectin and secrete it as a disulfide-bonded dimer composed of 230–270 kDa subunits. FN is one of the largest multi-domain proteins that interact with a variety of macromolecules like heparin, collagen /gelatin, and fibrin. FN is involved in many cellular processes, including tissue repair, embryogenesis, blood clotting, and cell migration/ adhesion and so can be used as a therapeutic agent for wound healing. In addition, its age-dependent increase in plasma and tissues may be accompanied in pathological states, especially in tumor growth, by its proteolytic breakdown.

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14-3-3, a family of acidic and soluble proteins, highly conserved in amino acid sequences from yeast to mammals, is expressed in all eukaryotic cells. Seven isoforms(β, γ, ε, η, ζ, σ and τ/θ) encoded by seven distinct genes are identified in mammals and forms homo- and hetero- dimeric cup-shaped structures. As 14-3-3 is interacted with more than 100 binding partners, it regulates key proteins involved in various biological processes such as signal trans-duction, cell cycle, transcriptional control, cell proliferation, apoptosis, and ion channel physiology. Most 14-3-3 requires phosphorylation of serine or threonine residues in the target sequence. This protein is abundantly expressed in the brain and has been detected in the cerebrospinal fluid of patients with different neurological disorders.

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α-fetoprotein (AFP) is a glycoprotein of 590 amino acids containing 3.4% carbohydrate content with a molecular weight of 61,000 – 75,000 Da. AFP is normally produced in the developing embryo and fetus by the fetal yolk sac, the fetal gastrointestinal tract, and eventually by the fetal liver. In humans, AFP levels decrease gradually after birth, reaching adult levels by 8 to 12 months. Normal adult AFP levels are low and AFP has no known function in normal adults.
The biologic role of AFP has not been defined yet. Because of its biochemical similarity to albumin, it has been postulated that AFP could be a carrier protein. It may have an immunoregulatory function during pregnancy.
Increased serum levels are found in some tumors, such as hepatocellular
carcinoma (HCC), hepatoblastoma, and germ cell tumors. Although total AFP is a useful serological marker for diagnosis of HCC, the false-negative or positive rate with AFP level is very high. AFP-L3, an isoform of AFP which binds Lens culinaris agglutinin, can be particularly useful in early identification of aggressive tumors associated with HCC. AFP mRNA, the circulating genetic markers, also has been used in monitoring distal metastasis or postoperative recurrence of HCC.

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Cyclin-dependent kinase-5 (CDK5) is a member of the cyclin-dependent kinase family of serine/threonine kinases. Its mRNA and protein are expressed in kidney, testes, and ovary. And Its activity is detected almost exclusively in brain extracts.
Similar to other Cdks, monomeric Cdk5 displays no enzymatic activity, but Cdk5 is not activated by cyclins. Instead, Cdk5 activity requires association with one of two brain-specific regulatory subunits called p35 and p39. The two activators regulate the spatial and temporal expression of active Cdk5 to restrict its activity primarily to post-mitotic neurons.

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The human Catecholamine-Sulfating Phenol Sulfotransferase (CSPS) is the only sulfotransferase that catalyses the sulfation of catecholamins, in particular the neurotransmitter dopamine, with high activity. CSPS is required for stimulation by Mn2+ of the sulfating activity and expressed in the human intestine, brain, platelet and other tissues. In the brain it may play a role in regulating the levels of dopamine. It also serves as a detoxifying function in the intestine, where it may detoxify potentially lethal dietary monoamines.

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Platelet-derived growth factors (PDGFs) have been implicated in the control of cell proliferation, survival and migration. The PDGF family of growth factors consists of five different disulphide-linked dimers built up of four different polypeptide chains encoded by four different genes. Theses isoforms, PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, act via two receptor tyrosine kinases, PDGF receptors α and β. Thus far, gene-targeting experiments have been attempted to create knockout mice deficient for PDGFR-α or PDGFR-β. Those mice, however, died either at the embryonic stage or several days after birth. Platelet-derived growth factor receptors, PDGFR-α and PDGFR-β, have five extracellular immunoglobulin-like domains and an intracellular tyrosine kinase domain. Upon binding a PDGF, the receptors form homo- and heterodimers. Dimerization of the receptors juxtaposes the intracellular part of the receptors, which allow phosphorylation in trans between the two receptors in the complex. These autophosphorylation provide docking sites for downstream signal transduction molecules. More than 10 different SH2–domain-containing molecules have been shown to bind to different autophosphorylation sites in the PDGF α- and β-receptors. There are signal transduction molecules with enzymatic activity, such as PI3-kinase, PLC-γ, Src, SHP-2, GAP, as well as adaptor molecules such as Grb2, Shc, Nck, Grb7 and Crk, and Stats. Each of the different partners recruited by the activated receptor initiates different signaling pathways, making possible a great variety of cellular response.

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Insulin receptor substrate (IRS) proteins play a central role in maintaining basic cellular functions such as growth and metabolism through insulin/insulin like growth factor (IGF) signaling. Four members (IRS-1, IRS-2, IRS-3, IRS-4) of this family have been identified which differ in their subcellular distribution and interaction with SH2 domain proteins. After phosphorylation by activated receptors, these intracellular signaling molecules recruit various downstream effector pathways including phosphatidylinositol 3-kinase, tyrosine protein phosphatase SHPTP-2, and several smaller adapter molecules such as the growth factor receptor-binding protein Grb-2.
IRS-1, the best characterized IRS protein, has eighteen potential tyrosine phosphorylation sites which directly bind to SH2 domains in downstrem proteins. IRS-1 consists of amino terminal containing pleckstrin homology (PH) domain followed by a phosphotyrosine-binding (PTB) domain which binds to IR and IGFR, and carboxy terminal containing multiple tyrosine and serine residues which become docking sites for proteins that have PTB domain such as SH2 domain.
IRS-4 is the last identified member of the IRS family. Cloning of human IRS-4 revealed a predicted protein of similar length to both IRS-1 and IRS-2and showed only 27% and 29% identity with IRS-1 and IRS-2, respectively. In contrast, IRS-4 exhibits higher degree of homology in the PH domain (43 to 50 %) and the PTB domain (43 to 66%) with the corresponding domains in IRS-1, IRS-2 and IRS-3.
IRSs are also thought to be able to induce malignant transformation. IRS-1 has been shown to be constitutively active in breast cancer.

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Attractin is a serum glycoprotein of 175 kDa and found in both membrane-bound and secreted forms as a result of alternative splicing. Both the secreted and membrane-bound forms of attractin may be involved in the development and maintenance of the central nervous system. Membrane-bound attractin is a co-receptor for Agouti, antagonist of melanocortin-1 receptor. Secreted attractin, expressed by activated T lymphocytes and modulates interactions between T cells and monocytes/macrophages, was examined as a potential marker of immune activity. Attractin may be a component of a pathway for regulated protein turnover that also involves mahogunin, a wide-expressed E3 ubiquitin ligase found at particularly high levels in the brain. Attractin was considered as an extracellular target amenable for the development of obesity-regulating drugs, also.

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The mammalian thioredoxin reductases (TrxRs) are a family of selenocysteine-containing pyridine nucleotide-disulfide oxido-reductases. All the mammalian TrxRs are homologous to glutathione reductase with respect to primary structure including the conserved redox catalytic site (-Cys-Val-Asn-Val-Gly-Cys-) but distinctively with a C-terminal extension containing a catalytically active penultimate selenocysteine (SeCys) residue in the conserved sequence(-Gly-Cys-SeCys-Gly). TrxR is homodimeric protein in which each monomer includes an FAD prosthetic group, a NADPH binding site and a redox catalytic site. Electrons are transferred from NADPH via FAD and the active-site disulfide to C-terminal SeCys-containing redox center, which then reduces the substrate like thioredoxin. The members of TrxR family are 55 – 58 kilodalton in molecular size and composed of three isoforms including cytosolic TrxR1, mitochondrial TrxR2, and TrxR3, known as Trx and GSSG reductase (TGR). TrxR plays a key role in protection of cells against oxidative stress and redox-regulatory mechanism of transcription factors and various biological phenomena (1).

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Superoxide dismutase (SOD) is an antioxidant enzyme involved in the defense system against reactive oxygen species (ROS). SOD catalyzes the dismutation reaction of superoxide radical anion (O2-) to hydrogen peroxide, which is then catalyzed to innocuous O2 and H2O by glutathione peroxidase and catalase. Several classes of SOD have been identified. These include intracellular copper, zinc SOD (Cu, Zn-SOD/SOD-1), mitochondrial manganese SOD (Mn-SOD/SOD-2) and extracellular Cu, Zn-SOD (EC-SOD/SOD-3) (1). SOD-1 is found in all eukaryotic species as a homodimeric 32 kDa enzyme containing one each of Cu and Zn ion per subunit (2). The manganese containing 80 kDa tetrameric enzyme SOD2, is located in the mitochondrial matrix in close proximity to a primary endogenous source of superoxide, the mitochondrial respiratory chain (3). SOD-3 is a heparin-binding multimer of disulfide-linked dimers, primarily expressed in human lungs, vessel walls and airways (4). SOD-4 is a copper chaperone for superoxide dismutase (CCS), which specifically delivers Cu to copper/zinc superoxide dismutase. CCS may activate copper/zinc superoxide dismutase through direct insertion of the Cu cofactor.

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Selenoprotein-P(SelP) is the major selenoprotein in human blood plasma and a transport protein which is carrying selenium to various extrahepatic tissues. Though its expression is detected in most tissues, highest amounts are produced by the liver, which secretes highly glycosylated SelP into plasma. Purification of human SelP yields two distinct isoforms with 61 and 55 kDa, differing in selenium content. SelP also has been shown to chelate heavy metals such as cadmium and mercury, and there are several evidences about its serum antioxidant capacity and protection against oxidative stress. Selenium deficiency predispose to several pathological condition such as cancer, coronary heart disease and liver necrosis although the biological function of SelP in various pathologic conditions has not been established.

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The Smad family of proteins are functioning in the transmission of extracellular signals in the TGF-β signaling pathway. Binding of a TGF-β superfamily ligands to extracellular receptors triggers phosphorylation of Smad2 at a Serine-Serine-Methionine-Serine (SSMS) motif at its C-terminus. Phosphorylated Smad2 is then able to form a complex with Smad4. These complexes accumulate in the cell nucleus, where they are directly participating in the regulation of gene expression.
In mammals, eight Smad proteins have been identified to date. The Smad family of proteins can be divided into three functional groups: the receptor-activated Smads (R-Smads), common mediator Smads (Co-Smads), and the inhibitory Smads (I-Smads). The R-Smads are directly phosphorylated by the activated type I receptors on their C-terminal Ser-Ser-X-Ser (SSXS) motif and include Smad1, Smad2, Smad3, Smad5, and Smad8. Smad2 and Smad3 are phosphorylated in response to TGF-β and activin, whereas Smad1, Smad5, and Smad8 are phosphorylated in response to BMP (Bone Morphogenetic Protein). This C-terminal phosphorylation allows R-Smad binding to Co-Smad, Smad4, and translocation to the nucleus where they regulate TGF-β target genes. Smad6 and Smad7 belong to the I-Smad which bind to the type I receptor or Smad4 and block their interaction with R-Smads.

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Glyceraldehyde-3-phosphate dehydrogenase(GAPDH) is a catalytic enzyme commonly known to be involved in glycolysis. The enzyme exists as a tetramer of identical 37-kDa subunits. GAPDH catalyzes the reversible reduction of 1,3-bisphosphoglycerate to glyceraldehyde 3-phosphophate in the presence of NADPH. Apart from playing a key role in glycolysis, this ubiquitously expressed enzyme also displays other activities unrelated to its glycolytic function. GAPDH is reported to be involved in the processes of DNA replication, DNA repair, nuclear RNA export, membrane fusion and microtubule bundling. Other studies also provide evidence of GAPDH playing an essential part of the program of gene expression observed in apoptosis and as part of the cellular phenotype of age-related neurodegenerative diseases. On recent study, GAPDH has identified of the most oxidant sensitive cell proteins.

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The Smad family of proteins are functioning in the transmission of extracellular signals in the TGF-β signaling pathway. Binding of a TGF-β superfamily ligands to extracellular receptors triggers phosphorylation of Smad2 at a Serine-Serine-Methionine-Serine (SSMS) motif at its C-terminus. Phosphorylated Smad2 is then able to form a complex with Smad4. These complexes accumulate in the cell nucleus, where they are directly participating in the regulation of gene expression.
In mammals, eight Smad proteins have been identified to date. The Smad family of proteins can be divided into three functional groups: the receptor-activated Smads (R-Smads), common mediator Smads (Co-Smads), and the inhibitory Smads (I-Smads). The R-Smads are directly phosphorylated by the activated type I receptors on their C-terminal Ser-Ser-X-Ser (SSXS) motif and include Smad1, Smad2, Smad3, Smad5, and Smad8. Smad2 and Smad3 are phosphorylated in response to TGF-β and activin, whereas Smad1, Smad5, and Smad8 are phosphorylated in response to BMP (Bone Morphogenetic Protein). This C-terminal phosphorylation allows R-Smad binding to Co-Smad, Smad4, and translocation to the nucleus where they regulate TGF-β target genes. Smad6 and Smad7 belong to the I-Smad which bind to the type I receptor or Smad4 and block their interaction with R-Smads.
The Smads share sequence similarities, most notably in the N-terminal and carboxy-terminal regions, referred to as the MH1 (Mad Homology 1) and MH2 domains respectively. Smad2 and Smad3 have 66% amino acid sequence identity between their MH1 domains and 96% amino acid sequence identity between their MH2 domains.