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Cellular retinaldehyde-binding protein (CRALBP) is a cytoplasmic protein, abundantly expressed in the retinal pigment epithelium (RPE) and Müller glia of the retina and in the pineal gland. Structurally, human CRALBP is a ∼36-kDa monomeric protein, proposed to adopt an “open” or “closed” conformation, depending on whether it is carrying an endogenous ligand. CRALBP interacts structurally and functionally with 11-cis-retinol dehydrogenase (RDH5), an enzyme of the visual cycle in RPE. CRALBP is a member of the CRAL_TRIO family of proteins that share a lipid-binding domain derived from the yeast Sec14 protein.
Mutations in the human CRALBP gene cause retinal pathology and delayed dark adaptation. CRALBP knockout mice have a delayed response in rhodopsin regeneration, 11-cis-retinal production and dark adaptation after illumination.

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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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The inhibitor of caspase-3-activated DNase (ICAD) is a caspase 3 substrate that controls nuclear apoptosis. ICAD has two isoforms: a functional isoform of 45kDa, ICAD-L/DNA fragmentation factor (DFF) 45; and a 35kDa isoform, ICAD-S/DFF35. Although both ICAD-L and ICAD-S can bind and inhibit CAD, only ICAD-L was reported to be functional. ICAD is cleaved to be inactivated and allow caspase-activated DNase (CAD) to execute nuclear internucleosomal apoptotic DNA fragmentation. In non-apoptotic cells, CAD is complexed with its inhibitor, ICAD. The activation of the CAD/ICAD complex occurs through the caspase 3-mediated
cleavage of ICAD at residues 117 and 224, which results in three ICAD fragments that are then released from CAD. In addition to its DNase
inhibitory activity, ICAD acts as a CAD specific folding chaperone. There are recent reports that ICAD is a potential target for restoring a normal apoptotic signal transduction pathway in colon and brain cancer cells.

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TAK1 (transforming growth factor-β-activated kinase 1) is a MAPKKK activated by TGF-β, or the pro-inflammatory cytokines TNF (tumour necrosis factor) and IL-1 (interleukin-1), or bacterial LPS (lipopolysacchar-ide). It plays a key role in switching on several pro-inflammatory signaling pathways, including those that activate the MAPKs (mitogen-activated protein kinases), termed p38α MAPK, JNK1/2 (c-Jun N-terminal kinase 1/2) and ERK1/2 (extracellular-signal-regulated kinase 1/2), as well as the transcription factor NFκB (nuclear factor κB).
TAB1 (TAK1-binding protein 1) is one of the regulatory subunits of TAK1 and plays a role as an activator of TAK1 in response to stimulation of ΤGF-β. TAB-1 can also mediate MKK-independent p38 kinase. Recently, induction of p38 autophosphorylation and consequent kinase activation by TAB1 expression in cultured neonatal cardiomyocytes have been reported.

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p38 MAPK cascade regulates a variety of cellular responses to stress, inflammation and other signals. p38 MAPK is relatively inactive in the non-phosphorylated form and becomes rapidly activated by dual phosphorylation of a Thr-Gly-Tyr motifs. There are four isoforms of p38 MAPK, , ,  and , which differ in their tissue expression and affinity for upstream activators and downstream effectors.
When cells are exposed to tumor necrosis factor-, interleukin-1, heat shock, or other activating stimuli, activation of MAPK kinase-3 and –6 occurs by phosphorylation. Activated MAPK kinase-3/6 phosphorylate each residue of Thr180 and Tyr182 in p38 MAPK. Phospho-p38 MAPK activates ATF-2, CHOP-1, MEF-2 and other transcription factors through phosphorylation.

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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). SOD1 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). SOD3 is a heparin-binding multimer of disulfide-linked dimers, primarily expressed in human lungs, vessel walls and airways (4). SOD4 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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Diazepam Binding Inhibitor(DBI) is a highly conserved 10 kDa polypeptide which is expressed in various species range from yeast to mammals. As an inverse agonist for benzodiazepine receptors, DBI downregulates inhibitory effects of GABA. It also has potential to induce anxiety. Found in central and peripheral tissues, DBI also participates in metabolism of steroids, which has been known to partially modify GABAA receptor function in the CNS. In peripheral tissues, DBI plays regulatory roles in steroidogenesis. DBI levels have been reported to be decreased in the cerebrospinal fluid obtained from patients with Alzheimer’s disease.

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Casein kinases are a group of ubiquitous Ser/Thr kinases that phosphorylate key regulatory proteins involved in the control of cell differentiation, proliferation, chromosome segregation, circadian rhythms, and metabolic pathways. CK1 family members share a highly conserved kinase domain but differ in their variable N- and C-terminal domains.
Mammals have seven family members: α, β, γ1, γ2, γ3, δ and epsilon. They all share at least 50% amino
acid identity within the protein kinase catalytic domain. CK1 isoforms exclusively use ATP as phosphate donor and are generally co-factor independent.
Casein kinase I epsilon is a Wnt-regulated kinase, and regulated phosphorylation of Dvl allows fine tuning of the Wnt-b-catenin signaling pathway. CKIe positively regulates Akt possibly by inhibiting PP2A. CKIe
play an important role in neurodegenerative diseases.

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Ferredoxin reductase is a ubiquitous flavoenzyme, containing noncovalently bound FAD as a prosthetic group (1). It plays a role in delivering NADPH or low potential one-electron donors such as ferredoxin and flavodoxin to redox-based metabolisms in plastids, mitochondria and bacteria (2). In mammals, ferredoxin reductase is loosely associated with the inner mitochondrial membrane and receives electrons from NADPH. These electrons are transferred to ferredoxin which shuttles electrons to cytochrome P450 in the adrenal cortex mitochondrial steroid hydroxylation systems (3).

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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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Methionine sulfoxide reductase B (MsrB), also known as SelX, is a selenoprotein. The oxidation of methionine at the sulfur atom leads to alternative epimers: R form of Met(O) and S form of Met(O). MsrB can reduce R form of both free and protein-incorporated methionine sulfoxide to methionine. It has a crucial role in protecting cells against oxidative damages.
MsrA reduces only the S epimer of Met(O), and MsrB reduces the R epimer of Met(O) in proteins. Although the catalytic mechanisms of MsrA and MsrB are similar, two Msrs have no sequence identity and no structural similarity.

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p53 is a transcription factor that regulates the cell cycle and hence functions as a tumor suppressor. p53 has been described as "the guardian of the genome", referring to its role in conserving stability by preventing genome mutation. p53 has many anti-cancer mechanisms: activating DNA repair proteins when DNA has sustained damage, holding the cell cycle at the G1/S regulation point on DNA damage recognition, initiating apoptosis if the DNA damage proves to be irrepairable. Human p53 is 393 amino acids long and has three domains: N-terminal transcription-activation domain (TAD), which activates transcription factors. 2) central DNA-binding core domain (DBD) 3) C-terminal homo-oligomerisation domain (OD); tetramerization greatly increases the activity of p53 in vivo. Mutations that deactivate p53 in cancer usually occur in the DBD and most of these mutations destroy the ability of the protein to bind to its target DNA sequences.
The activity of p53 is regulated at different levels and includes control by multi-site phosphorylation. p53 is phosphorylated (Ser6 and Ser9) by casein kinase 1δ and casein kinase 1ε both in vitro and in vivo.

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C reactive protein(CRP) is a major acute phase reactant synthesized primarily in the liver hepatocytes. It is a pentraxin(cyclic pentameric protein) compound of five identical nonglycosylated subunits of 206 amino acids each(M.W 24kDa) that are bound noncovalently to form the physiologic CRP molecule(M.W. 117.5kDa). CRP binds to several nuclear components, including chromatin and histones. This may indicate that it functions as a scavenger during cell necrosis. CRP also appears to have the strongest association with cardiovascular events; It may, therefore, be associated with ischemic heart disease. Its rapid increase in synthesis within hours after tissue injury or infection suggests that it contributes to host defense and that it is part of the innate immune response.

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Syk, Spleen tyrosine kinase, is expressed in a wide range of hematopoietic and non-hematopoietic cells and plays a key role in adaptive immune system, which is the immunoreceptor (B cell receptor and Fc-receptors) signaling pathways including Fcγ receptor-mediated phagocytosis. In hematopoietic cells such as B and T lymphocytes, natural killer cells, mast cells, macrophages and platelets, Syk is involved in the proximal signaling downstream of activated immunoreceptors (e.g. BCR, TCR, Fc receptors) containing immunoreceptor tyrosine-based activation motifs (ITAMs) to which it binds using its tandem SH2 domains. Activated and autophosphorylated Syk then phosphorylates its specific substrates including other enzymes and adaptor proteins, orchestrating a complex series of cellular responses such as cell proliferation, differentiation, survival and phagocytosis.

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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.
Human complement factor C8 is one of five components (C5b, C6, C7, C8, and C9) that interact to form the cytolytic membrane attack complex (MAC) which is the cytolytic end product of the complement cascade. MAC is typically formed on the surface of intruding pathogenic bacterial as a result of the activation of the complement system, and it is one of the ultimate weapons of the immune system.
C8 is composed of an α (64 kDa), β (64 kDa), and γ (22 kDa) subunit. Within C8, the subunits are arranged as a disulfide-linked C8 α-γ heterodimer that is noncovalently associated with C8 β. During MAC formation, C8 α mediates binding and self-polymerization of C9 to form a pore-like structure on the membrane of target cells.

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Paraoxonases are a group of enzymes invloved in the hydrolysis of organophosphates. Paraoxon, an organophosphate, is an acetylcholinesterase inhibitor and the active metabolite of the insecticide parathion. Besides a toxicological role, clinical interest has focused on a protective role in vascular disease.
Paraoxonase-1 (PON1) is a calcium-dependent ester hydrolase that is tightly associated with apoA-I in HDL. PON1 prevents the oxidation of LDL, thereby the formation of atherogenic oxidised-LDL.
Polymorphisms of the human PON1 gene are correlated with coronary artery disease, indicating a genetic association between PON1 and coronary artery disease. PON1 activity is lower in subjects prone to development of atherosclerosis such as in type 1 and type 2 diabetes, familial hypercholesterolemia, and renal disease, indicating the involvement of PON1 in atherosclerosis development.
PON2 is a ubiquitously expressed intracellular protein that can protect cells against oxidative damage.
PON3 is similar to PON1 in activity but differs from it in substrate specificity.
PON1 and PON3 are implicated in lowering the risk of developing coronary artery disease and atherosclerosis. Human PON3 protein shares the 3 conserved cysteine residues identified in PON1, suggesting their importance of in vivo activities.
PON1-based catalytic scavengers can be a way to safe and effective organophosphate intoxication.

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Plasminogen, a 92kDa glycoprotein, is produced by the liver and is present in plasma and extracellular fluids. Plasminogen is the inactive precursor of plasmin, a potent serine protease involved in the dissolution of fibrin blood clots. Plasminogen can be converted into the active plasmin by plasminogen activators urokinase (uPA), tissue plasminogen activator (tPA), factor XII-dependent components. The plasmin system has been implicated in a variety of physiological and pathological processes such as fibrinolysis, tissue remodeling, cell migration, inflammation, and tumor invasion and metastasis. Hereditary defects of plasminogen is a predisposing risk factor for thromboembolic disease.

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Green fluorescent protein (GFP) isolated from jellyfish Aequorea aequorea is a 238 amino acid protein with an apparent molecular weight of about 27-30 kDa on SDS-PAGE. Its chromophore is formed by cyclisation and oxidation of the three amino acids Ser65, Tyr66, and Gly67.
The numerous applications include : using GFP as a reporter for gene expression, as a marker to study cell lineage during development and as a tag to localize proteins in living cells. Other applications of GFP include assessment of protein protein interactions through the yeast two hybrid system and measurement of distance between proteins through fluorescence energy transfer (FRET) protocols. GFP technology has considerably contributed to a greater understanding of cellular physiology.

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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.

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Tau proteins are microtubule-associated proteins that are abundant in neurons in the central nervous system. In adult human brain, there are six tau isoforms that differ by the presence of either three or four C-terminal tandem repeated 31 or 33 amino acid sequences containing domains that are important for microtubule binding. Tau plays a crucial role in the neuron as it binds and stabilizes microtubules, and can regulate axonal transport; functions that are regulated by site-specific phosphorylation events. Abnormally hyperphosphorylated Tau protein, resulting in loss of function (the disruption of axonal transport) and gain of toxic function (formation of tau aggregates) at the same time, is deposited in cells as fibrillar lesions in numerous neurodegenerative diseases such as Alzheimer's disease, progressive supranuclear palsy, Pick's disease, corticobasal degeneration and post-encephalitic parkinsonism.

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Both Chk1 and Chk2 are critically important checkpoint kinases. Chk1 is essential for normal development and cell growth and Chk1 deficiency in mouse or in embryonic stem (ES) cells is lethal. Loss of Chk2 is tolerated and has been found to be associated with a subset of Li-Fraumeni cases. Li-Fraumeni syndrome increases greatly the susceptibility to cancer, with particularly high occurrences of breast cancer, brain tumors, acute leukemia, soft tissue sarcomas, bone sarcomas, and adrenal cortical carcinoma.
Chk2 regulates cell cycle checkpoints and apoptosis in response to DNA damage, particularly to DNA double-strand breaks. The cell either stops the cell cycle and therefore its proliferation until the damage is repaired, or it destructs itself (apoptosis).
The ataxia telangiectasia mutated (ATM) and ATR (ATM and Rad3-related) protein kinases exert cell cycle delay, in part, by phosphorylating Chk1, Chk2, and p53. Phosphorylation on Chk1 and p53 requires ATR, whereas phosphorylation on Chk2 requires ATM.
Screening of novel substrates of Chk1 and Ckh2 followed by imunoprecipitation kinase assay and site-directed mutagenesis analysis suggests that HDAC5 and PGC-1 are specific targets for Chk1 and/or Chk2 at least in vitro.

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IκB kinase β (IKKβ) is a component of a multiprotein kinase complex that regulates the activity of the transcription factor NF-κB. Activation of the IKK complex via upstream stimuli leads to phosphorylation and degradation of NF-κB bound IκB (Inhibitor of κB). Subsequently, free NF-κB dimers enter the nucleus and regulate the transcription of a variety of target genes involved in cell proliferation and differentiation, apoptosis, and inflammation, etc. The IKK complex consists of 2 highly homologous kinase subunits, IKKα and IKKβ, and a nonenzymatic regulatory component, IKKγ/NEMO. The relative contributions of IKKα and IKKβ to the signaling complex vary according to the requirements of the cell. IKKβ plays a predominant role in immune responses, while IKKα alone appears to be sufficient for at least some developmental systems. Recently, IKK/NF-κB signaling pathway was studied as therapeutic targets in cancer.

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Enolase (2-phosphogly-cerate hydrolyase or phosphopyruvate hydrates) is a glycolytic enzyme that catalyzes the dehydration and conversion of 2-phosphoglycerate to phospho-enolpyruvate. It comprises three distint subunits, alpha, beta and gamma. The gamma-gamma and alpha-gamma dimeric forms of enolase, referred to as neuron-specific enolase(NSE), are localized mainly in neurons and neuroectodermal tissue. NSE has a high stability in biological fluids and can easily diffuse to the extracellular medium and cerebrospinal fluid(CSF) when neuronal membranes are injured. NSE is used clinically as a sensitive and useful marker of neuronal damage in several neurological disorders including stroke, hypoxic brain damage, status epilepticus, Creutzfeldt-Jakob disease, and herpetic encephalitis.

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Receptor protein tyrosine phosphatase rho (RPTPρ/PTPRT) is a transmembrane protein that is highly expressed in the developing and adult central nervous system. It is a member of the RPTP R2B subfamily, which includes PTPκ, PTPμ and PCP-2. The R2B phosphatases are known to interact with members of the cadherin/catenin complex.
These four RPTPs share the same domain structure: an extracelluar domain, a juxtamembrane region, and two phosphatase domains. The extracellular domain of PTPR mediates cell-cell aggregation and that mutational inactivation of this phosphatase could promote tumor migration and metastasis. PTPRT is the most frequently mutated PTP in human cancers. STAT3 is a substrate of PTPRT. Phosphorylation of a tyrosine at 705 is essential for the function of STAT3, and PTPRT specifically dephosphorylated STAT3 at this position.

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The inter-α-trypsin inhibitor (ITI, IαI) family, a typical and classical example for protein-glycosaminoglycanprotein (PGP) complexes, occurs constitutively in plasma at relatively high concentrations and is a result of alternate combinations of three kinds of heavy chains with a common light chain, the bikunin proteoglycan. Bikunin has two proteinase inhibitor domains and belongs to the Kunitz-type protease inhibitor family; it displays an inhibitory activity against trypsin, leukocyte elastase and plasmin. The heavy chains do not have any protease inhibitory properties but have the capacity to interact in vitro and in vivo with hyaluronic acid and this binding promotes the stability of the extra-cellular matrix. The ITI protein family is suspected of playing a key role in the extra-cellular matrix biology.

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Fibronectins bind cell surfaces and various compounds including collagen, fibrin, heparin, DNA, and actin. Fibronectins are involved in cell adhesion, cell motility, opsonization, wound healing, and maintenance of cell shape.

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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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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 nucleotide binding 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 the other two kinases, MEK1/2, which in turn phosphorylates tyrosine/threonine in 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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The casein kinase I (CKI) family of serine/threonine protein kinases is highly conserved from yeast to humans. The CKI family is involved in many diverse and important cellular functions, such as regulation of membrane transport, cell division, DNA repair, circadian rhythms, and nuclear localization.
The name of the enzyme family was originated from the convenience of casein as a substrate since the earliest days of research on protein phosphorylation.
Casein kinase 2 (CK2) is a ubiquitous, highly conserved, essential serine/threonine kinase which has been implicated in cell cycle control, DNA repair, regulation of the circadian rhythm and other cellular processes.
CK2 is a tetramer of two α subunits and two β subunits. The α subunits have the catalytic kinase domain. Loss of the α‘ catalytic subunit produces male infertility, and loss of the single β regulatory subunit is
early embryonic lethal.
CK2 appears to be upregulated in most cancers and the promotion of tumorigenesis by the overexpression of CK2 has been reported in transgenic mice.

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Catalase is a homotetrameric heme-containing enzyme present within the matrix of all peroxisomes. It carries out a dismutation reaction in which hydrogen peroxide is converted to water and oxygen. Human catalase has the last four amino acids (-KANL) at the extreme C-terminus for peroxisome targeting. The monomer of human catalase is 61.3 kDa in molecular size. Catalase has been implicated as an important factor in inflammation, mutagenesis, preven-tion of apoptosis, and stimulation of a wide spectrum of tumors. Loss of catalase leads to the human genetic disease, acatalasemia, or Takahara’s disease (1).