Effects of 8-azaguanine on riboflavin production and on the nucleotide pools in non-growing cells of Eremothecium ashbyii.

Abstract

The effects of a guanine analogue, 8-azaguanine, on the riboflavin biosynthesis and the nucleotide pools were examined using non-growing cell systems of flavinogenic and non-flavinogenic strains of E. ashbyii. 1) 8-Azaguanine, as such, strongly inhibited riboflavin formation at low concentrations. The halfway inhibition point was detected at 5×10-5 M. 2) The inhibition of riboflavin biosynthesis by 8-azaguanine was completely overcome by the supplementation of purines. Xanthine gave the most efficient recovery from this inhibition. 3) Fluctuation of the nucleotide pools in non-growing cells of flavinogenic and non-flavinogenic strains were examined using Dowex 1×2 (formate) in the presence of 8-azaguanine 18 hr after start of incubation. As a result, five new peaks appeared on the chromatogram in the flavinogenic strain whilst only one new peak was observed in non-flavinogenic strain. Furthermore, with the addition of xanthine with 8-azaguanine, peaks I, II and IV disappeared from the column, peak III was unchanged and peak V decreased to a fair extent. 4) Five peaks in flavinogenic strain were identified to be (I) uridine, (II) 8-azaguanine, (III) guanosine, (IV) 8-azaguanosine and (V) 8-azaguanosine triphosphate in the order of elution from the column and one peak in non-flavinogenic strain was found to be 8-azaguanine.