One unit will hydrolyse 1,0 µmole of N-alpha-benzoyl-L-arginine ethyl ester (BAEE) per minute at 25 °C and pH 6,2.

Papain is a Sulphhydryl protease from Carica papaya latex.

It is used in dissecting solutions. It is used to produce Fab fragments of antibodies. It is used for cell dissociation since it has been shown to be more effective and less damaging with certain tissues. It has been used to isolate morphologically intact cortical neurons from postnatal rats. Limited papain digestion is used for structural studies of enzymes and other proteins. In addition, it is used in red cell serology to modify the red cell surface to enhance or destroy the reactivity of many red cell antigens. It is useful for platelet serology studies. It has also been used in the enzymatic synthesis of amino acids, peptides, and other molecules.

Papain is a cysteine protease that cleaves peptide bonds of basic amino acids, leucine, or glycine. It is also hydrolyses esters and amides.