Studies on the biosynthesis of riboflavin. 7. The incorporation of adenine and guanine into riboflavin and into nucleic acid purines in Eremothecium ashbyii and Candida flareri

It is now well established that, after removal of C-8, purines are actively incorporated into rings B and c of riboflavin (see e.g.Goodwin, 1959; Plaut, 1961a, b).Further, the addition of purines to cultures of the flavinogenic fungi Eremothecium ashbyii and Candidaflareri stimulates the synthesis of riboflavin (Goodwin & Pendlington, 1954; Goodwin & McEvoy, 1959).In E. ashbyii guarine is more effective than xanthine, the purine structur- ally most similar to riboflavin, and both are more effective than adenine, whereas hypoxanthine is least effective (Brown, Goodwin & Jones, 1958).In C. flareri guanine and xanthine are both actively flavinogenic, but adenine and hypoxanthine, although supporting growth, have no flavinogenic action (Goodwin & McEvoy, 1959).The work described below was undertaken in an attempt to explain the varying effects of the different purines in the two micro-organisms.Before this could be done it was necessary to prepare biosynthetically uniformly labelled (U) [U-14C]adenine and [U-_4C]guanine.The only purines available commercially were labelled in C-8, which is lost when the purines are converted into riboflavin.A short account of part of this work has already appeared (Audley, Goodwin & McEvoy, 1959).EXPERIMENTAL Organisms.Eremothecium ashbyii used throughout was the original strain of Goodwin & Pendlington (1954).The culture was maintained at room temperature on agar slopes containing (g./100 ml.): agar, 1-5; D-glucose, 1 0; bacterio- logical peptone, 1-0; yeast extract, 0-1.Subcultures were made every 2 weeks.The liquid medium used was that described by Goodwin & Pendlington (1954), with bacterio- logical peptone added to a concentration of 0 04%.After adjustment to pH 5-8, the medium was autoclaved at 15 lb./in.2 for 15 min.The strain of Candida flareri used throughout was NRRL 245, kindly provided by the North Regional * Part 6 (Goodwin & Horton, 1960).