VITAMINS

Flavobacterium sp. 238-7 excreted a considerably high amount of vitamin B_6 i.e. 20 μg/ml, in the form of pyridoxine into the culture medium. The cellular productivity was higher than that of other microorganisms. A resting cell system of vitamin B_6 biosynthesis was developed. In screening of compounds effective for improvement of the vitamin production, some nucleosides and nucleotides were found to have a strong stimulating effect on the biosynthesis. Some amino acids were also effective. Though the addition of glycolaldehyde did not increase the amount of vitamin B_6 in the system, a significant enzyme activity for reduction of glycolate to glycolaldehyde was found in a membrane fraction of the cell free extract. The enzyme catalyzed the reduction but not the oxidation, namely the reverse reaction, and was therefore designated as glycolate reductase. A positive correlation was observed between the enzyme activity and the biosynthesis of vitamin B_6 during the cultivation. The high vitamin productivity of the bacterium could be explained by lack of regulation of vitamin B_6 biosynthesis in the growing and resting cell systems and by that of glycolate reductase.

View full abstract

In order to clarify the photobleaching process of the visual pigment rhodopsin by chemical methods, two kinds of rhodopsin analogues [(XIb) and (XII)] were synthesised. The former was derived from 9-cis-retro-γ-retinal (Xb) having two dissected chromophoric systems, one diene and one trienal chromophore. The latter was prepared from 11-cis-locked cyclopentatrienylidene retinal (IV). From the photochemical behaviours of two artificial visual pigments [(XIb) and (XII)] at low temperatures, the conversion of rhodopsin to bathorhodopsin-the primary photochemical event-was confirmed not to involve the proton translocation mechanism but to be caused by the isomerisation of the 11, 12-cis-double bond to trans geometry. Circular dichroism observations in the two 11-cis-fixed-rhodopsin analogues [(XIb) and (XII)] have demonstrated that the origin of the optical activity of rhodopsin in the visible region should be due to the twisted conformation around the 12-13 single bond.

View full abstract

A kinetic equation for methionine formation from homosysteine with B_<12>-dependent methionine synthetase was deduced from the well-known scheme proposed by Weissbach and Taylor. The appropriateness of the equation was examined experimentally in the reaction system with the enzyme from Escherichia coli 215 cultivated in the presence of CN-B_<12>. The action of various corrinoids on the methionine formation was evaluated with respect to the kinetic parameters involved in the equation. CH_3-B_<12> showed a high affinity for the enzyme and a high catalytic activity for formation of holoenzyme compared with those of CN-B_<12>. DBCC had a low activity for methionine synthesis, while fluoromethyl phosphito-P-cobalamin, a high activity. 2-Amino-2-methyl-1-propanol cyanocobalamin and cobalt free corrinoid strongly inhibited the reaction.

View full abstract

Show abstractHide abstract

Vitamin D_2 in Shiitake (Lentinus edodes) was identified and determined. The results obtained were as follows : (1) Vitamin D_2 in Shiitake was identified by HPLC, UV spectrum and GCMS, whereas 25-OH-D_2 could not be detected in it. (2) The HPLC-method reported previously (J. Nutr. Sci. Vitaminol., 30, 11-25, 1984) was confirmed to be also useful for the determination of vitamin D_2 in Shiitake. The recovery and coefficient value were 102.5±4.8 (M±SD)% and 4.6%, respectively, which were satisfactory. (3) The assayed values of vitamin D_2 In raw Shiitake (No.1 and 2) cultured outdoors (averages: 310 and 390_<IU>/100g) were higher than those cultured in a vinylhouse (73_<IU>/100g). In the case of dried Shiitake, vitamin D_2 values obtained Koshin cultured and picked up in September (the shape of pileus is spread, 969_<IU>/100g) were higher than those in Donko cultured and picked up in February (the shape of pileus is closed, 300_<IU>/100g). The results suggested that vitamin D_2 in Shiitake was photochemically produced from ergosterol during cultivation by solar radiation. (4) The assayed values of ergosterol in the samples of shiitake mentioned above were much higher than those of vitamin D_2 (about 6,500〜46,000 times as weight ratio). (5) Vitamin D_2 was not solubilized into water by Soaking or boiling of dried Shiitake with water. However, the content of vitamin D_2 decreased gradually during boiling, which suggested that the vitamin was not solubilized into water but destroyed during boiling. On the other hand, the vitamin was not destroyed by oil cooking (Fried with an oil for 2 min or in an oil for 1 min).

View full abstract

Download PDF (804K)

Register with J-STAGE for free!