STUDIES ON HUMAN C'1-ESTERASE. II. FUNCTION OF PURIFIED C'1-ESTERASE IN THE HUMAN COMPLEMENT SYSTEM.

It was concluded that C′1-esterase is a functional component of complement and that esterolytic activity and C′4 inactivation may be functions of the same catalytic site.

Abstract

Summary Purified C′1-esterase inactivated both C′2 and C′4 in solution. Esterolytic activity and the ability to inactivate C′4 could not be dissociated by inactivation of the enzyme with C′1-esterase inhibitor or DFP, or by denaturation at extremes of temperature or pH. It was concluded that these activities were in all probability properties of the same molecular species. Inhibition of enzymatic activity by DFP blocked both the ability to inactivate C′4 and the ability to bind C′1-esterase inhibitor, suggesting in addition that esterolytic activity and C′4 inactivation may be functions of the same catalytic site Purified C′1-esterase was capable of substituting for C′1s in the formation of EAC′1 with C′1q and C′1r. EAC′1 prepared with C′1-esterase was capable of forming EAC′1,4 with partially purified C′4. It was therefore concluded that C′1-esterase is a functional component of complement.