Activation of bovine factor VII (proconvertin) by factor XIIa (activated Hageman factor)

Abstract

Bovine factor VII (proconvertin) is a plasma glycoprotein that participates in the extrinsic pathway of blood coagulation. It has a MW of 45,500 and is composed of a single polypeptide chain with an amino-terminal alanine residue. Factor VII is readily converted to factor VIIa by factor XIIa (activated Hageman factor) employing an enzyme to substrate weight ratio of 1:50. Factor VIIa is composed of a L and H chain held together by a disulfide bond(s). The H chain, which is formed from the carboxyl-terminal region of the precursor, contains an aminoterminal sequence of Ile-Val-Gly-Gly-. The H chain also contains the active-site sequence of -Phe-Cys-Ala-Gly-Tyr-Thr-Asp-Gly-Thr-Lys-Asp-Ala-Cys-Lys-Gly-Asp-Ser-Gly-Gly-Pro-His-. This sequence is homologous with the active-site region of a number of plasma serine proteases. Factor VII is a typical precursor of a serine protease which is converted to an enzyme by factor XIIa by the cleavage of a single, internal peptide bond.