The possibility whether guanine ribonucleotidyl-(3'-5')-adenosine (G
pA) is accumulated or not was studied with the use of micro-organisms such as
E. ashbyii (a non-flavinogenic strain),
E. coil, S. cerevisiae and
N. crassa, which produce riboflavin in a trace amount. (1) In a flavinogenic strain of
E. ashbyii, riboflavin formation was stimulated fivefold in the presence of glucose (1%) compared with that in the control experiment without glucose. The presence of caffeine notice-ably restricted riboflavin formation during incubation of non-growing cells with or without glucose. Moreover, the addition of caffeine to the glucose-free medium brought about marked accumulation of G
pA in the cells.
(2) In a non-flavinogenic strain of
E. ashbyii, riboflavin formation was remarkably slight under normal conditions. The effect of glucose and caf-feine on flavinogenesis in the same strain was much smaller than that in the flavinogenic strain except for the case of the glucose-free medium supple-mented with caffeine. However, compound (G
pA) never accumulated in the strain, even under conditions permitting a large amount accumulation of G
pA in a flavinogenic strain.
(3) The other organisms,
E. coil, S. cerevisiae and
N. crassa, did not accu-mulate G
pA in the cells under the same conditions as those with a high flavinogenic strain of
E. ashbyii.
(4) The results obtained indicated that a dinucleotide, G
pA, is a com-pound closely related to the biosynthesis of riboflavin.
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