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JBC, Vol. 251, Issue 20, 6238-6243, Oct, 1976
C. T. Esmon and J. W. Suttie
Vitamin K is required for an enzymatic carboxylation of glutamyl residues
in a microsomal protein precursor of plasma prothrombin to form
gamma-carboxyglutamic acid. The enzyme system (carboxylase) which catalyzes
this reaction has now been solubilized by extraction of the microsomes with
Triton X-100 and has been shown to fix H14CO3- as gamma-carboxyglutamic
acid residues in biologically active prothrombin. Enzyme activity requires
O2 and vitamin K hydroquinone or vitamin K + NADH. Unlike the
microsomal-bound carboxylase, soluble carboxylase activity is independent
of either ATP or Mg2+ addition and is unaffected by either the ATP analog,
adenyl-5'-yl imidodiphosphate (AMP-P(NH)P, or EDTA. These observations
suggest that the energy required to drive the carboxylation reaction is
derived from the oxidation of the reduced form of vitamin K. Although the
membrane-bound carboxylase is inhibited by Warfarin, this anticoagulant is
ineffective as an inhibitor of the soluble enzyme. A second anticoagulant,
2-chloro-3-phytyl-1,4-natpthoquinone (chloro-K), differs from Warfarin in
that it effectively inhibits both the membrane-bound and soluble
carboxylases.
Vitamin K-dependent carboxylase. Solubilization and properties
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