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  • Title: Vitamin B-12 deficiency increases the specific activities of rat liver NADH- and NADPH-linked aquacobalamin reductase isozymes involved in coenzyme synthesis.
    Author: Watanabe F, Nakano Y, Tachikake N, Saido H, Tamura Y, Yamanaka H.
    Journal: J Nutr; 1991 Dec; 121(12):1948-54. PubMed ID: 1941258.
    Abstract:
    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.
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