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Studies on the Molecular Basis for Cs Action and Comparison of Cs with Other Tryptic Proteases

Center for Blood Research, Boston, Mass., and Stanford, Research Institute, Menlo Park, Calif

Abstract

One of the principal problems in current complement research is our understanding of the molecular basis of complement action. In order to probe the molecular biology and specificity of the serine protease, Cs, it was compared with three human proteases. The proteases examined were the serum enzymes C7s, thrombin and plasmin, and the pancreatic enzyme trypsin. An assay procedure using the simple synthetic chromophoric esters N-carbobenzoxy-L-tyrosine-p-nitrophenyl ester and N-carbobenzoxy-L-lysine-p-nitrophenyl ester as substrates was developed. A group of over 20 mono- and di-substituted benzamidines, known as competitive inhibitors of bovine tryptic enzymes, were used to probe the active sites.

The inhibition constants obtained were correlated with factors describing the lipophilicity and electronic character of the inhibitors using multiparameter regression analysis. Marked similarities were noted between Cs and the other enzymes. The difference between the enzymes with respect to their inhibition profiles can be interpreted on a molecular basis to account for some of the specificity shown by these enzymes.