Some properties of proteinase b in the venom of Agkistrodon halys blomhoffii

Abstract The properties of proteinase b (endopeptidase) isolated from the venom of snake, Agkistrodon halys blomhoffii , were studied. Proteinase b contained approx, 2 g-atoms of calcium per molecule as estimated by atomic absorption spectrophotometry and spectrophotometric titration with EDTA. After the removal of the calcium by electrodialysis or by treatment with EDTA (10 −2 M), the resulting enzyme molecule underwent some conformational change, followed by loss of the proteolytic activity. This conformational change and the concomitant loss of enzyme activity were found to be irreversible. The activity of venom proteinase b was slightly inhibited by -SH reagents, including p -chloromercuribenzoate (PCMB), monoiodoacetic acid, N -ethylmaleimide and 5,5′-dithio-bis-(2-nitrobenzoic acid). On prolonged incubation with the enzyme, PCMB caused significant inhibition. In the presence of 8 M urea and 10 −2 M EDTA, one mole of -SH group was found per enzyme molecule, while in the absence of urea and EDTA, only 20% of the -SH group was measurable. Thus, it may be suggested that the metal is probably involved in the stabilization of the enzyme molecule, and that the -SH groups are closely related to the enzyme activity of proteinase b .