Immunological aspects of the binding of substrate analogues and polypeptide inhibitors to α-chymotrypsin

Abstract

The effects of substate analogues and various polypeptide inhibitors on the immunological behavior of α-chymotrupsin have been observed by means of quantitative complement fixation. The interaction of α-chymotrypsin with substrate analogues produced a slight increase of the complement fixed over that fixed by α-chymotrypsin alone. The immunological effects of the interaction of α-chymotrypsin with polypeptide inhibitors were not uniform. Soybean and basic pancreatic inhibitors showed very little, in any, effect on complement fixation. An inhibitor isolated from the navy bean (phaseolus vulgaris) produced a shift of the complement fixation curve to the left with nearly double the maximum amount of complement fixed. Complement fixation by chymotrypsinogen with rabbit anti-α-chymotrypsin sera, was much greater than that produced by α-chymotrypsin itself. It is possible that some chymotrypsinogen was present in the α-chymotrypsin used for immunization. Both the substrate and the polypeptide inhibitors were per se without any effect either on the anti-α-chymotrypsin antibodies or on the lytic activity of the complement, or on the complement fixation produced by nonrelated immunological systems. A conformational change of the enzyme upon the interaction with substrate analogues and the navy bean inhibitor may explain this immunochemical behavior of α-chymotrypsin.