ENZYMATIC NATURE OF HUMAN CLR - SUBCOMPONENT OF THE 1ST COMPONENT OF COMPLEMENT

Abstract

Esterase activity of C1.hivin.r [r fragment of activated complement component 1] was investigated. C1.hivin.r hydrolyzed 2 amino acid methyl esters (N-acetyl-L-arginine methyl ester and N-acetyl-glycyl-L-lysine methyl ester) and 2 amino acid p-nitrophenyl esters (N-carbobenzyloxy-L-tyrosine-p-nitrophenyl ester (N-Z-L-Tyr-ONp and N.alpha.-carbobenzyloxy-L-lysine-p-nitrophenyl ester)). Detailed kinetic analysis of N-Z-L-Tyr-ONp hydrolysis by C1.hivin.r revealed that the enzymatic activity 1.mu.g of protein decreased as C1.hivin.r concentration was increased. Activity loss suggested that above 0.5 .mu.M C1.hivin.r was undergoing aggregation with an active site loss. When C1.hivin.r was titrated with the active site titrant p-nitrophenyl-p''-guanidinobenzoate the titratable site number/mg of protein decreased with increasing protein concentration. N-Z-L-Tyr-ONp hydrolysis by C1.hivin.r was inhibited by several synthetic inhibitors including phenylmethanesulfonylfluoride, p-amidinophenylmethanesulfonylfluoride, DFP and p-tosyl-L-lysine-chloromethyl ketone. The peptide esterase inhibitors Trasylol, hirudin, leupeptin and C.hivin.1 esterase inhibitor had no effect on C1.hivin.r esterase activity.