Activation of coagulation Factor V by calcium-dependent proteinase

Abstract

Factor V is a key coagulation cofactor, regulating the rate of Factor X a-catalyzed prothrombin conversion. Activation of Factor V markedly accelerates coagulation. This study describes a new class of Factor V activators, sulfhydryl proteinases. Of the enzymes studied, calcium-dependent proteinase was the most effective activator. Activation of Factor V by this enzyme was associated with cleavage of 125I-labeled Factor V to peptides distinct from those generated by previously described activators. Calcium-dependent proteinase-activated Factor V a peptides with molecular weights of 114 000 and 93 000 bound both to Factor X a and to cultured endothelial cells. Calcium-dependent proteinase was identified in vascular endothelial cells, a tissue that also synthesizes Factor V. These findings suggest a previously unknown mechanism for cellular regulation of coagulation.