The effect of polycations on the activity of pepsin

A study has been made of the interaction of selected polycations with pepsin A (E.C. 3.4.23.1). Protamine, polybrene, spermine, spermidine and poly(L-lysine) all acted as inhibitors of the enzyme at low concentrations, but at higher concentrations of the polycations the inhibition was less pronounced. A more detailed study of the anomalous inhibition was made using protamine, polybrene and poly(L-lysine) and it was shown experimentally that, when used by themselves, each of these polycations acted as a weak proteolytic catalyst. The order of catalytic effectiveness was: protamine greater than polybrene much greater than poly(L-lysine). Thus, it is now possible to explain why the observed inhibition of pepsin decreases when the concentration of the inhibiting polycation is increased.