title: Vitamin K-dependent carboxylase: evidence for a semiquinone radical intermediate.
abstract: Nanosecond laser flash photolysis has been used to produce and identify the vitamin K semiquinone (radical) from vitamin K dihydroquinone and to observe its formation and decay in the presence of vitamin K-dependent carboxylase (epoxidase). The activity of vitamin K-dependent carboxylase is not decreased by exposure to the laser. Absorbance of the semiquinone is proportional to enzyme concentration and is stimulated by a synthetic substrate, Phe-Leu-Glu-Glu-Ile. Stabilization of the semiquinone is observed in the presence of the enzyme. The semiquinone is rapidly destroyed in the presence of inhibitors of vitamin K-dependent carboxylase and vitamin K epoxidase.
mesh_terms: D000818:Animals; D019735:Carbon-Carbon Ligases; D005609:Free Radicals; D007700:Kinetics; D007834:Lasers; D008025:Ligases / Q000378:metabolism*; D008297:Male; D010777:Photochemistry; D051381:Rats; D011919:Rats, Inbred Strains; D014812:Vitamin K / Q000031:analogs & derivatives* / Q000378:metabolism; D010837:Vitamin K 1 / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D005609:Free Radicals; D014812:Vitamin K; C041103:vitamin K semiquinone radical; C028843:vitamin K1 hydroquinone; D010837:Vitamin K 1; D008025:Ligases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase