VITAMINS

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[I] Synthesis and vitamin C activity of L-threo-hexo-2-enaro-1,4-lactone (S-AsA) have been studied. (i) S-AsA was almost quantitatively obtained by the hydrolysis of 6-carboxyascorbic acid-2-sulfate (S-AsS) for 10 min at 100℃, which, in turn, was prepared by the selective oxidation of ascorbate-2-sulfate (AsS) over platinum black. (ii) The oxidative cleavage of S-AsS with bromine formed 6-carboxydehydroascorbic acid, of which intermediate gave S-AsA by the reduction with hydrogensulfide in a 65% yield. [II] The antiscorbutic activity of sodium salt of S-AsA (S-AsA・Na) was examined by the three methods in Hartley guinea pigs fed on a vitamin C deficient diet. (i) The antiscorbutic activity of S-AsA・Na was compared with that of equimolar AsA orally administered. (ii) Hartley guinea pigs, which had been fed on a vitamin C deficient diet and resulted in scurvy, were divided two groups. Each group was orally administered with AsA and equimolar S-AsA・Na, respectively. Recovery tests from the scurvy of these two groups were carried out. (iii) Because the guinea pig receiving S-AsA・Na suffured from scurvy, treatment effects of the double dose of S-AsA・Na orally administered and intraperitoneally injected were compared with those of AsA. The results of this investigation indicate that the close relationship may exist between structure of C-6 position of ascorbic acid analogues and the development of vitamin C activity, although S-AsA・Na does not prevent and cures scurvy in the guinea pig.

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Intestinal uptake of riboflavin was studied kinetically in details by using everted intestinal rings of rats. In ^<14>C-riboflavin uptake to intestinal rings, two mechanisms were proved; the linear component due to diffusion and the saturable component which predominates at concentrations less than 0.5μM and is against concentration gradients. By the Lineweaver-Burk plots, K_m values and V_<max> were shown to be 0.13 μM and 0.55 nmol/g tissue/15 min. The saturable component was influenced by additions of metabolic inhibitors such as 2,4-dinitrophenol, KCN, and NaF, but the linear component was not. Neither of the two components were inhibited by ouabain. The uptake in the linear component were enhanced by bile salt (taurocholate) and Tween 80, but those of the saturable component were not.

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