Comparative distribution, metabolism, and utilization of phylloquinone and menaquinone-9 in rat liver.
The liver of most species contains a spectrum of bacterially produced menaquinone homologs as well as the major dietary form of vitamin K, phylloquinone. The relative utilization of phylloquinone and menaquinone-9 (MK-9) as substrates for the microsomal vitamin K-dependent gamma-glutamyl carboxylase was determined in a rat model. Vitamin K 2,3-epoxide, the co-product of the carboxylation reaction, is recycled to the quinone form of the vitamin by a microsomal vitamin K epoxide reductase. This enzyme activity was blocked by warfarin administration, and the appearance of the hepatic epoxides of phylloquinone and MK-9 was determined as a measure of their utilization by the carboxylase. When the liver contained equimolar amounts of phylloquinone and MK-9, four times as much phylloquinone epoxide as MK-9 epoxide was present in the liver 1 hr after warfarin administration. These data suggest that hepatic MK-9 is not as efficiently utilized as phylloquinone. The data obtained have also demonstrated a previously unrecognized difference in phylloquinone and menaquinone metabolism. MK-9 epoxide, and to a lesser extent MK-9, was preferentially localized in the mitochondria, while higher concentrations of phylloquinone were found in the microsomes.
Reedstrom
C K
CK
Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706, USA.
Suttie
J W
JW
D000818:Animals; D019735:Carbon-Carbon Ligases; D004032:Diet; D008025:Ligases / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014812:Vitamin K / Q000031:analogs & derivatives* / Q000378:metabolism; D010837:Vitamin K 1 / Q000031:analogs & derivatives / Q000378:metabolism*; D024482:Vitamin K 2 / Q000031:analogs & derivatives*; D014859:Warfarin / Q000494:pharmacology
D024482:Vitamin K 2; D014812:Vitamin K; C016186:vitamin K1 oxide; C073355:menaquinone 9; D014859:Warfarin; D010837:Vitamin K 1; D008025:Ligases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase