Endogenous proteinase activity

Trypsin is a major proteolytic digestive enzyme and the identified endogenous ligand for proteinase-activated receptor 2 (PAR 2). 

Overdigestion of tissue is common when proteinase-K or triton is used to improve antigen retrieval penetrance of the primary antibody. The easiest correction is to dilute triton solutions and decrease the time of the proteinase-K incubation. Tissue can also be digested when the hydrogen peroxide solution, used to quench endogenous peroxidase activity, is left on too long or is too concentrated. To correct this, check... 

Fig. 9. Regulation of thiol proteinase activities by endogenous inhibitor. P, Thiol proteinase I, endogenous inhibitor.

The absence of specific 1,25-(0H)2[ H]D3 binding activity in HL-60 cell preparations is due to proteolysis of the 1,25-(0H)2[ H]D3 receptor (Inaba and DeLuca 1989). An endogenous proteinase may act on the steroid-binding domain of the 1,25-(0H)2D3 receptor or in its immediate vicinity, because it destroyed the l,25-(OH)2D3-binding ability of unoccupied receptor, but did not digest occupied receptor. The proteinase appeared to belong to the serine class of proteases, which is specifically inhibited with diisopropylfluorophosphate and not hydrolysed diisopropylfluorophosphate. 

Pinter, M., and Friedrich, P., 1988, The calcium dependent proteolytic system calpain-calpatatin in Drosophila melanogaster, Biochem J., 253, 467-473 Pinter, M., Stierandova, A., and Friedrich, P., 1992, Purification and characterization o a Ca2 activated thiol protease from drosophila melanogaster, Biochemistry, 31, 8201-8206 Pontremoli, S., Melloni, E., Michetti, M., Salamino, F., Sparatore, B., Horecker, B., 1988, An endogenous activator of the Ca2+ -dependent proteinase of human neutrophils that increases its affinity for Ca2+, Proc. Natl. Acad. Sci., USA, 85, 1740-1743... 

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