Ribitol and flavinogenesis in Eremothecium ashbyii.
1. Supplementation of cultures of Eremothecium ashbyii with ribitol leads to a twofold increase in riboflavin formation compared with unsupplemented cultures or those supplemented with ribose or ribulose phosphate. Addition of unlabelled ribitol decreases the incorporation of [1-(14)C]ribose into riboflavin, indicating that free ribitol is preferred to ribose for incorporation into riboflavin. 2. The enzymes ribitol kinase, d-ribose reductase, d-ribose 5'-phosphatase and GMP nucleosidase were demonstrated in the cell-free extracts. Ribitol induces the formation of ribitol kinase. The enzyme is activated in vitro by the flavinogenic purines, guanine and xanthine. d-Ribose reductase shows a specific requirement for NADPH and forms free ribitol from ribose. 3. The activities of ribitol kinase, ribose 5'-phosphatase and GMP nucleosidase reach their maximal values before riboflavin formation reaches a maximum. 4. [U-(14)C]GMP is taken up intact by the culture of E. ashbyii and is incorporated into riboflavin as well as into a blue fluorescent compound. The radioactivity from this compound is incorporated into riboflavin by the cell-free extract of E. ashbyii.
D001203:Ascomycota / Q000201:enzymology / Q000378:metabolism*; D002247:Carbon Isotopes; D002854:Chromatography, Paper; D004789:Enzyme Activation; D006147:Guanine; D006150:Guanine Nucleotides; D009249:NADP; D010088:Oxidoreductases; D010770:Phosphotransferases; D011687:Purines; D012256:Riboflavin / Q000096:biosynthesis*; D012266:Ribose / Q000378:metabolism*; D014970:Xanthines
D002247:Carbon Isotopes; D006150:Guanine Nucleotides; D011687:Purines; D014970:Xanthines; D009249:NADP; D006147:Guanine; D012266:Ribose; D010088:Oxidoreductases; D010770:Phosphotransferases; D012256:Riboflavin