The present experiments were carried out to investigate the relation between sugar metabolism and riboflavin formation in nongrowing cells of Eremothecium ashbyii incubated with various sugars (related compounds) and purines.
Glycerol, gluconate and glucono-o-lactone markedly stimulated riboflavin formation with increasing concentrations up to 0.5% or with increasing incubation times, but above the concentration range the effects of these substances on flavinogenesis were different. Ribose, xylose and ribitol brought about a weak stimulation of riboflavin formation in a concentration range of 0-0.2%. Glucose and fructose enhanced flavinogenesis in a concentration range of 0-0.5% but were inhibitory above the range. Glucosamine strongly restricted riboflavin formation in lower concentrations and the inhibition effect occurred immediately after its addition. The inhibition of riboflavin formation due to glucosamine (0.15%) was almost completely recovered by glucose (1.0%) but not by glycerol. Caffeine (5mM) reduced the yields of riboflavin to a fairly greater extent. The decrease was reversed not by xanthine, guanine and theobromine but by glycerol, ribose and glucose, especially by glycerol (0.5%). Accordingly, caffeine was considered to inhibit a pentose phosphate pathway and glucosamine to inhibit a glycolytic pathway closely related to flavinogenesis.