Abstract
First, mention was made that G Compound (2, 4-dioxo-6, 7-dimethyl-8-ribityl-pteridine) and V Compound (2, 4-dioxo-6-methyl-7-hydroxy-8-ribityl-pteridine), isolated from the culture product of Er. ashbyii, were renamed 6, 7-dimethyl-ribolumazine and 6-methyl-7-hydroxy-ribolumazine, respectively.
6, 7-Dimethyl-ribolumazine was assumed to be an intermediate in the biosynthesis of riboflavin on the basis of the results of chemical studies by Masuda and biochemical studies by Katagiri, et al. It has been recognized by many researchers that purine compounds play an important role in the biosynthesis of riboflavin. It has also been assumed that when a purine compound is added prior to the cultivation of Er. ashbyii, its C-8 is not utilized for the biosynthesis and that the pyrimidine nucleus enters as such in the isoalloxazine nucleus. So the authors investigated the relationship between 6, 7-dimethyl-ribolumazine and purine compounds, especially uracil derivatives which are the degradation products of purines.
Formation of 6, 7-dimethyl-ribolumazine is readily understood if it is considered that 4, 5-diaminouracil, a compound lacking C-8 of xanthine, is first produced, and a ribityl group then enters N-4 of the product to give 4-ribitylamino-5-aminouracil, which in turn reacts with diacetyl or with acetoin. Therefore, if such a uracil derivative is isolated from the culture products of Er. ashbyii, it is most powerful to prove the route of the biosynthesis, but in reality the formation of such a compound has not been confirmed.
According to the authors' studies, the addition of 4, 5-diaminouracil prior to the cultivation of Er. ashbyii rather checked the formation of riboflavin and neither 6, 7-dimethyl-lumazine nor lumichrome could be detected. When 4-methyl-amino-5-aminouracil instead of 4, 5-diaminouracil was added, 6, 7, 8-trimethyl-lumazine was found in the broth. In spite of the fact that this lumazine derivative readily reacts with diacetyl in vitro to give lumiflavin, no lumiflavin could be detected in the above broth. Hence, it should be considered that when a uracil derivative is converted to riboflavin via a lumazine compound, it is utilized for the biosynthesis only when its NH2 at C-4 is substituted by a ribityl group.
