Mailänder B, Bacher A
J Biol Chem. 1976 Jun 25;251(12):3623-8.
We studied the incorporation of 14C-labeled guanosine into riboflavin under conditions precluding the metabolic conversion of guanosine compounds to free guanine. For this purpose we isolated a mutant BM 2 of Salmonella typhimurium deficient in the enzymes IMP dehydrogenase, purine nucleoside phosphorylase, and purine nucleotide pyrophosphorylase. The mutant incorporated [ribose-14C]guanosine into riboflavin and GMP without dilution. The isolated compounds were exclusively labeled in the ribityl and ribosyl side chain, respectively. AMP and CMP were not labeled. [2-14C]Guanosine was incorporated into riboflavin and GMP without dilution. The isolated compounds were exclusively labeled in the isoalloxazine and guanine moiety, respectively. AMP and CMP were again unlabeled. We conclude that the ribose moiety of proffered guanosine is directly converted to the ribityl moiety of riboflavin. Thus the biosynthesis of the vitamin begins at the level of a guanosine compound. Guanine, ribose, ribitol, and the respective phosphates are not direct precursors of the vitamin.
我们研究了在排除鸟苷化合物向游离鸟嘌呤代谢转化的条件下，将14C标记的鸟苷掺入核黄素的情况。为此，我们分离出了鼠伤寒沙门氏菌的一个突变体BM 2，该突变体缺乏肌苷酸脱氢酶、嘌呤核苷磷酸化酶和嘌呤核苷酸焦磷酸化酶。该突变体将[核糖-14C]鸟苷掺入核黄素和鸟苷酸中且未被稀释。分离出的化合物分别仅在核糖醇基和核糖基侧链上被标记。腺苷酸和胞苷酸未被标记。[2-14C]鸟苷被掺入核黄素和鸟苷酸中且未被稀释。分离出的化合物分别仅在异咯嗪和鸟嘌呤部分被标记。腺苷酸和胞苷酸再次未被标记。我们得出结论，提供的鸟苷的核糖部分直接转化为核黄素的核糖醇部分。因此，维生素的生物合成始于鸟苷化合物水平。鸟嘌呤、核糖、核糖醇和各自的磷酸盐不是维生素的直接前体。
