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MM Huh, BP Schick, PK Schick and RW Colman
Department of Medicine, Temple University School of Medicine, Philadelphia
19140.
Coagulation factor V (FV) has been shown to be synthesized in both the
liver and megakaryocytes. We now present evidence that FV can be covalently
crosslinked by an enzyme originating from megakaryocytes to form polymeric
multimers of factor V. The guinea pig megakaryocyte enzyme appears to be
factor XIIIa since the FV-crosslinking activity (1) had an absolute
requirement for Ca++, (2) was completely inhibited by iodoacetamide,
5,5'-dithiobis- (2-nitrobenzoic acid), p- chloromercuribenzene sulfonic
acid, and N-ethylmaleimide, all known alkylators of the thiol group at the
active site of the factor XIIIa, (3) was blocked by known pseudoamine donor
substrates of factor XIIIa including dansylcadaverine and putrescine, and
(4) could be directly demonstrated in the guinea pig megakaryocyte lysate
by a specific activity staining procedure. No tranglutaminase was detected
in guinea pig megakaryocytes in contrast to red cells and liver. A similar
pattern of covalent crosslinking of human FV by purified activated human
plasma factor XIII was also demonstrated. Analysis of the crosslinked
products of FV formed by the guinea pig enzyme by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicates the
formation of intermediate as well as higher molecular weight polymers,
suggesting that the crosslinking is a stepwise polymerization process.
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