Studies on the 4-carbon compound needed for the formation of the O-xylene ring of riboflavin.

Acta vitaminologica et enzymologica Pub Date : 1985-01-01
K Nakajima
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Abstract

The 4-carbon compound necessary for the formation of the o-xylene ring of riboflavin, was examined using labeled glucose and diacetyl in resting cells of Eremothecium ashbyii. The specific activity-time curves of riboflavin and lumichrome in the tracer experiments with [U-14C] glucose indicated that the specific activity of riboflavin during the incubation is much higher than that of its photolytic product, lumichrome. It is far above the level expected if the ribityl moiety of an intermediate, 4-ribitylamino-5-amino-2,6-dihydroxy-pyrimidine (RAADP), was to be utilized as the source of the 4-carbon unit on the o-xylene ring of riboflavin. It was further demonstrated that the specific activities of diacetyl and lumichrome at 10.5 h of the incubation and those of crystalline riboflavin and lumichrome at the later stage (20 h) of the incubation were identical respectively. Radioactive diacetyl furthermore proved to be likewise incorporated with a two fold dilution into riboflavin and lumichrome at 17 h of the incubation. The results reveal that it is not the ribityl fragment of RAADP bu the diacetyl that is the 4-carbon unit for the formation of the pyrazine ring of 6,7-dimethyl-8-ribityllumazine, that is, the o-xylene ring of riboflavin in the mold of Eremothecium ashbyii, although we still do not know whether the diketone requiring reaction is enzymatic or non-enzymatic.

核黄素o -二甲苯环形成所需的4碳化合物的研究。
用标记的葡萄糖和双乙酰在静息细胞中检测了核黄素o-二甲苯环形成所必需的4碳化合物。[U-14C]葡萄糖示踪实验中核黄素与光色色素的比活性-时间曲线表明,核黄素在培养过程中的比活性远高于其光解产物光色色素。如果利用中间体4-核糖基氨基-5-氨基-2,6-二羟基嘧啶(RAADP)的核糖基部分作为核黄素的邻二甲苯环上的4碳单元的来源,则远高于预期的水平。进一步证明,在培养10.5 h时,双乙酰和光色胺的比活性与结晶核黄素和光色胺在培养后期(20 h)的比活性相同。放射性双乙酰进一步证明同样与核黄素和光色在孵育17小时稀释两倍。结果表明,虽然我们还不清楚需用二酮的反应是酶促反应还是非酶促反应,但形成6,7-二甲基-8-ribityllumazine的吡嗪环的4碳单元不是RAADP的ribityl片段,而是二乙酰基。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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