Vitamin B-12 deficiency increases the specific activities of rat liver NADH- and NADPH-linked aquacobalamin reductase isozymes involved in coenzyme synthesis.
Rat liver contains both NADH- and NADPH-linked aquacobalamin reductases, which are involved in the synthesis of the vitamin B-12 coenzymes and are distributed in both the mitochondrial and microsomal membranes. To clarify the physiological roles of these hepatic enzymes, vitamin B-12-deficient rats were used to study the effect of the deficiency on the enzyme activities. Male rats fed a vitamin B-12-deficient diet for 11 wk developed a severe vitamin B-12 deficiency with a high urinary methylmalonate excretion (214.3 +/- 115.2 mumol/d) and approximately 96% lower hepatic vitamin B-12 content. Tissues of the vitamin B-12-deficient rats were assayed for NADH- and NADPH-linked aquacobalamin reductase activities. The specific activities of both enzymes in homogenates of liver, kidney or upper intestine were shown to be three- to 20-fold greater in the vitamin-deficient rats than in the control rats. In liver, the vitamin deficiency specifically elevated the specific activities of the mitochondrial NADH-linked and microsomal NADPH-linked enzymes. These are likely the isozymes involved in vitamin B-12 coenzyme synthesis.
Watanabe
F
F
Laboratory of Nutrition and Food Science, Hagoromo-gakuen College, Osaka, Japan.
Nakano
Y
Y
Tachikake
N
N
Saido
H
H
Tamura
Y
Y
Yamanaka
H
H
D000818:Animals; D001835:Body Weight; D003067:Coenzymes / Q000096:biosynthesis; D007527:Isoenzymes / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D008297:Male; D008764:Methylmalonic Acid / Q000652:urine; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014806:Vitamin B 12 Deficiency / Q000201:enzymology / Q000378:metabolism*
D003067:Coenzymes; D007527:Isoenzymes; D008764:Methylmalonic Acid; C068157:aquacobalamin reductase; D009247:NADH, NADPH Oxidoreductases