The present study was planned to investigate whether the ratio of FAD, FMN, FR in liver changes by supplying of the different dietary protein levels or not. Male albino rats of the Wistar strain were used. The results showed that the total riboflavin and FAD contents of liver rose as casein level increased, but in low or non-protein diets, the total riboflavin in liver was significantly decreased. It was found that the ratio of each flavin compound in liver was same as that in normal dietary protein level, even under the conditions such as the nitrogen balance crumbles. It was suggested from these results that although the total metabolism may scale down by feeding of low or non-protein diet, a definite mechanism may act to reserve flavoprotein necessary to maintain the metabolism in accordance with the protein intake.

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It is an interesting fact that pyridoxal and toxopyrimidine having pyridine ring and pyrimidine ring respectively, were phosphorylated by the same phosphokinase of mouse brain as presented in previous paper. In this report, the substrate specificity of the pyridoxal kinase was studied. It was found that the highly purified enzyme could phosphorylate pyridoxine, pyridoxamine, 4- or 5-deoxypyridoxine, 2-methylmercapto-4-amino-5-hydroxymethylpyrimidine and 2-ethyl-4-amino-5-hydroxymethylpyrimidine, besides pyridoxal and toxopyrimidine, but did not phosphorylate pyrithioxine.

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A rapid transport and the accumulation of O-acetoglycoloyl-S-furoylthiamine (AFT) in human red cells were found and the detailed mechanism was investigated. AFT-^<35>S and thin layer chromatography were employed to clarify the metabolism of AFT in and outside the red cells and a rapid decomposition of AFT to undiffusible thiamine in the cells was found to be responsible for the accumulation phenomenon. S-Furoyl group was found to be decomposed mainly in non-enzymatic way, by intracellular glutathione, while O-acetoglycoloyl group by intracellular, and to a lesser extent by membrane, esterase, only the latter being strongly inhibited by di-isopropylfluorophosphate.

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The following nicotinic acid derivatives of the vitamin B_6 group have been prepared : Pyridoxine-5-nicotinate, pyridoxine-4,5-dinicotinate, 4-nicotinylpyridoxamine-5-nicotinate, 4-nicotinylpyridoxamine, pyridoxamine-5-nicotinate and pyridoxal-5-nicotinate. The ultraviolet absorption spectra of these compunds are essentially identical, with the exception of that of pyridoxal-5-nicotinate, which is distinguished by having a maximum at 390mμ in phosphate buffer (pH 7.0) as a solvent. Pyridoxine-5-nicotinate and pyridoxine-4,5-dinicotinate showed the vitamin B_6 activity for Sacch. carlsbergensis.

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Progress of the formation of riboflavin compounds of glucosyl oligosaccharide from sucrose and riboflavin by intracellular or extracellular enzyme preparations from Leuconostoc mesenteroides giving a high yield of riboflavin compounds of glucosyl oligosaccharide was followed by the paper chromatographic analysis. The synthesis of 5'-D-riboflavin-α-D-glucopyranoside (B_2-glucoside) reached the maximum value in earlier stage of incubation, and thereafter it was decreased, while riboflavin compounds of glucosyl oligosaccharide were produced by receiving glucosyl group successively from sucrose during the decrease of riboflavin glucoside. It was also pointed out that the intracellular enzyme preparation had both riboflavin compounds-producing and decomposing activities.

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The present paper deals with the experiments on the isolation and identification of riboflavin compounds of glucosyl oligosaccharide produced by the action of extracellular enzyme prepared from Leuconostoc mesenteroides NRRL B-1299. By the multiple paper chromatography in a macroscale, seven kinds of riboflavin compounds of glucosyl oligosaccharide were separated, and they were revealed chemically and enzymatically to be 5'-D-riboflavin-α-D-glucopyrano-side, two kinds of riboflavindisaccharides (kojibioside-like substance and isomaltoside), two kinds of riboflavintrisaccharides (glucosyltrisaccharide and dextrantrioside), riboflavin tetrasaccharide and riboflavinpentasaccharide, respectively. By the action of extracellular enzyme, moreover, riboflavin compounds of higher members of glucosyl oligosaccharide were obtained through successive transfer of glucosyl group between sucrose and riboflavin compounds of glucosyl oligosaccharide.

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The mechanism of coordination of organic bases to the cobalt atom of corrin ring was studied in the biosynthesis of corrinoids with the growing as well as resting cells of Propionibacterium arabinosum. 2-Monochloroadenyl cobamide (MCAC) produced was increased with the amounts of 2-monochloroadenine(MCA) added, depressing the formation of Ψ-B_<12> which is a main product of the microorganism without addition of any base, although the excessive MCA resulted in inhibition of MCAC production and in formation of various carboxylic acids of corrinoids. Even if adenine was added in the presence of MCA, no satisfactory restored formation of Ψ-B_<12> could not be obtained. In every case, a small, but approximately a definite amount of cobalamin was recognized. It means that a definite amount of 5,6-dimethylbenzimidazole(DBI) was always synthesized under the conditions employed and competitively incorporated into the corrinoid molecule. Further, when MCA, adenine and DBI were simultaneously added to the medium for biosythesis, a marked evidence was obtained for indicating that DBI was the strongest, MCA the second, and adenine the weakest cordinating bases to Co in the biosynthesis of corrinoids. A very good agreement was obtained between the results with the growing and resting cells.

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Riboflavin-2^<14>C and its tetrabutyrate were injected to rats and the excretion of riboflavin into urine was studied. In the case of riboflavin-2^<14>C injection (400μg. total counts 2.19×10^5cpm), 301.6μg (total counts 4.89×1.0^4 cpm) of riboflavin was excreted into urine during 24 hours after the injection. In the case of riboflavin tetrabutyrate-2^<14>C injection (400μg, total counts 2.19×10^5cpm), only 182.0μg (total counts 1.74×10^4cpm) of riboflavin was excreted into urine during 72 hours after the injection. These results confirmed the previously reported fact that riboflavin-^<14>C moiety of riboflavin tetrabutyrate-^<14>C is effectively incorporated into FAD and FMN of organs and stayed in animal body for a long time.

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A microbiological assay of vitamin B_6 with a pulp disk plate technique was performed. A pulp disk plate technique and the tube assay were performed with Saccharomyces carlsbergensis 4228. The values of vitamin B_6 was successfully determined in the liver of rat ingested with a routine diet and a vitamin B_6 deficient diet. A pulp disk plate technique and the tube assay showed similar results. Pulp disk plate method was simpler than tube assay technique but the former was less favorable for the determination with small quantity of material because it was difficult to fix the material on the disk.

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Mechanism of absorption, tissue distribution and metabolism of O, S-dicarbethoxythiamine (DCET) in rats were investigated by using ^<35>S-labelled DCET. DCET was quickly absorbed from intestine, the absorption rate reached to approximately 83% within 3 minutes when 233 μg of DCET was administered into the ligated sac of intestine in situ. O-carbethoxy group of DCET was readily metabolized in the intestine and absorbed in the form of S-carbethoxythiamine (CET), then reached the tissues where it is metabolized to thiamine. Presence of CET, along with thiamine diphosphate, in tissues such as liver, kidney and skin of rats administered DCET orally, intraperitoneally or intravenously was demonstrated by zone electrophoresis. At 2 hours after intraperitoneal injection of DCET, about 9% of total radioactivity was found in liver, 12% in muscles and 0.1 to 1% in skin, kidney, brain and heart. The radioactivity in muscles remained for a longer time than that in other tissues.

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