Cathepsin G can produce a gla-domainless protein C in vitro

Human polymorphonuclear leucocyte cathepsin G was used in vitro to digest human protein C. Anticoagulant assays showed that the proteinase affected a rapid loss in the anticoagulant activity of the zymogen. Calcium ions almost totally protected the anticoagulant activity of protein C against the action of cathepsin G. Polyacrylamide gel electrophoresis, in the presence of SDS (non reducing conditions), indicated that the proteolytic action of cathepsin G lead, to the removal of a peptide of low molecular mass (PC-L'') from protein C with the consequent formation of a product of high molecular mass (PC-P). Electrophoresis in the presence of SDS (reducing conditions) showed that the PC-L'' fragment was removed from the light chain of protein C (PC-L). N-terminal amino acid analysis of the PC-P product and COOH terminal amino acid analysis of PC-L'' product confirmed that cathepsin G had cleaved position Phe40:Trp41 in the light chain. This cleavage was responsible for removal of the gamma-carboxyglutamic acid (gla) containing region of protein C.