title: Vitamin K-dependent carboxylase. Stoichiometry of vitamin K epoxide formation, gamma-carboxyglutamyl formation, and gamma-glutamyl-3H cleavage.
abstract: The rat liver microsomal vitamin K-dependent carboxylase catalyzes the carboxylation of peptide-bound glutamyl residues to gamma-carboxyglutamyl (Gla) residues with the concomitant formation of vitamin K 2,3-epoxide (KO). These studies have demonstrated that the half-reaction, formation of KO, occurs in the absence of carboxylation at low glutamyl substrate concentration but that the ratio of KO/Gla approaches unity as the glutamyl substrate concentration is increased. Utilization of the carboxylase substrate Phe-Leu-[gamma-3H] Glu-Glu-Leu has demonstrated that the ratios of KO/gamma-C-H bonds cleaved and Gla/gamma-C-H bonds cleaved are equivalent at high substrate concentrations and that these ratios approach unity. At low substrate concentrations, KO formation occurs at a higher rate than gamma-H bond cleavage. These data are consistent with a mechanism involving the formation of an oxygenated intermediate from vitamin KH2 and O2 that is converted to KO during hydrogen abstraction from the gamma-position of the Glu substrate. In the absence of a Glu substrate, the intermediate is converted to KO by a mechanism not coupled to glutamyl activation.
authors.affiliation: Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706.
authors.forename: G M
authors.initials: GM
authors.lastname: Wood
authors.forename: J W
authors.initials: JW
authors.lastname: Suttie
mesh_terms: D015055:1-Carboxyglutamic Acid / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002244:Carbon; D019735:Carbon-Carbon Ligases; D005971:Glutamates / Q000378:metabolism*; D006859:Hydrogen; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D017693:Sodium Bicarbonate; D010837:Vitamin K 1 / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D005971:Glutamates; C016186:vitamin K1 oxide; D015055:1-Carboxyglutamic Acid; C028843:vitamin K1 hydroquinone; D002244:Carbon; D006859:Hydrogen; D010837:Vitamin K 1; D017693:Sodium Bicarbonate; D012964:Sodium; D008025:Ligases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase; D011190:Potassium Cyanide