Coagulation factor V exists uncomplexed in bovine plasma.

Abstract

Bovine coagulation factor V has been examined immunochemically to ascertain whether the coagulant polypeptide (h) with Mr = 290,000-330,000 is complexed in plasma with a second immunochemically distinct polypeptide (l2) of Mr = 400,000. Antiserum containing antibodies to h and l2 detects the l2 polypeptide eluting earlier than the h chain on gel filtration of plasma with either added calcium of EDTA, consistent with the behavior of a higher molecular weight noninteracting species. An immobilized monospecific antibody to l2 removes only the l2 polypeptide from a purified factor V preparation containing both h an l2. Moreover, while a monospecific antibody to the h chain was able to precipitate purified radioactively labelled h chain alone or mixed with plasma, the l2 antibody was unable to precipitate radioactively labelled h chain even after attempted recombination of the h chain with l2 present in plasma. These studies indicate that the l2 polypeptide is not complexed to the h chain in a purified system or in plasma and reinforce the conclusion that factor V is a single polypeptide chain uncomplexed in plasma.