Lipoamide dehydrogenase contains FAD and redox-acitve disulfide in its active center. The enzyme accepts two electron or four electrons under various conditions. In this paper we describe the electron transfer reaction mechanisms of NADH : lipoate reductase, NADH :osygen reductase, and NADH : menadione reductase. The enzyme catalyzed a mixed one-electron and two-electron reduction of oxygen and menadione, the two-electron transfer mechanism being dominant. The oxidase reaction is associated with fully-reduced flavin, and the menadione reductase reaction with half-reduced flavin. Furthermore, the superoxide radical generated by various reactions of the enzyme can reduce consecutively ferritin iron.

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It has been reported that vitamin K plays an important role in bone formation in vivo. But the mechanism is still veiled. We investigated the effect of an active form menaquinone-4 (MK-4, 2-methyl-3-all-trans-tetraprenyl-1, 4-naphtoquinone ; menatetrenone) on human osteoblastic function. Human osteoblasts derived from ulnar periosteum which show various characteristic features for osteoblasts, were cultured in α-MEM containing 10% fetal bovine serum. When confluent cells were exposed to MK-4 (2.25×10^<-6>M) in the presence of 2mM α-glycerophosphate for 21 days, mineralization in the cells was enhanced by the treatment. MK-4-induced mineralization was facilitated by the addition of 10^<-8> or 10^<-9> M 1,25-dihydroxyvitamin D_3, in which the effect had been already seen on day 5 of the treatment. The accumulation of osteocalcin, the vitamin K-dependent bone Gla protein, on cell layer was enhanced by MK-4 treatment, while the osteocalcin released into medium was not enhanced by the treatment. On the other hand the production of prostaglangin (PG) E_2, one of bone resorbing agents, was inhibited by MK-4 treatment. Our data suggested that the mineralization in osteoblasts induced by MK-4 was probably caused by the enhancement of osteocalcin accumulation on cell layer, and that MK-4 not only enhanced mineralization, but also might inhibit bone resorption by the inhibition of PGE_2 production. Both the enhancement of mineralization and the inhibition of PGE_2 production in human osteoblasts may contribute to the stimulative effects of MK-4 on bone formation in vivo.

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Daily vitamin E intakes of 7- healthy Japanese elderly subjects, over 60 years of age, were calculated from 3-day food records collected during middle of October, 1991, at six institutions in Tokyo and Kanagawa Prefecture, using the Japanese Food Composition Tables. The average vitamin E intakes were 6.6 ± 2.2 mg for men and 6.1 ± 1.8 mg for women, with a widely individual variation. The difference between maximum and minimum intake was 5.3 times for men and 4.5 times for women. The 73.8% of men and 68.1% of women failed to attain the vitamin E allowance of Japanese Recommended Dietary Allowance (RDA). There was a significantly positive correlation (r=0.488 for men and r=0.645 for women) between vitamin E intakes and total food intakes. In this study, poor dietary vitamin E intake in elderly men and women was pointed out, because the average vitamin E intakes for these age groups are generalley below the corresponding RDA. It may be recommended that vitamin E rich food, such as fats and oils, fishes, and green and yellow coloured vegetables, will be taken in the elderly peoples to surpass the RDA.

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Because of the difficulty of determination of vitamin B_2 in the lens, the normal values of the total amount and the three forms of vitamin B_2 in the lens of rat have not been demonstrated yet. The author have deviced that the assay method of vitamin B_2 and its derivatives in the single lens of rat after trypsin digestion combined with warm-water extraction using HPLC. It was found that the normal value of total amounts and the three forms of vitamin B_2 in rat lens were 0.318 ± 0.017 and FAD 0.276 ± 0.014, FMN 0.036 ± 0.008 and RF 0.006 ± 0.002 μg/g lens, respectively.

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