STUDIES ON INOSINE FERMENTATION - PRODUCTION OF INOSINE BY MUTANTS OF BACILLUS SUBTILIS .V. SPECIFIC REQUIREMENT OF ADENINE FOR REGULATION OF INOSINE FORMATION AND ADENINE-SPARING ACTION OF AICA AND AMINO ACID MIXTURE

Inosine formation by mutants of B. subtilis in chemically defined medium was investigated, using strains No. 11413 (adenine-histidine-requiring) and No. 11023-4 (adenine-requiring). Only adenine (or its congeners) regulates the formation of inosine in the growing culture, and adenine is a specific requirement for inhibition of inosine formation by non-growing washed cells of these mutants. Purines other than adenine, pyrimidines, and amino acids did not inhibit inosine formation by these washed cells. However, the optimum concentration of adenine for the nucleoside formation in growing culture was greatly altered by certain substances; AICA [5-amino-4-imidazolecarboxamide] and amino-acid mixture (artificial L-amino acid mixture of "casamino acids" type) have a strong adenine-sparing action, while AICA-R [riboside], L-histidine, purines, etc., had no such action. The AICA sometimes inhibited the adenine deamination reaction of the intact cells which might be one of the mechanisms of the sparing actionof the amine. The effect of the amino acid mixture on the deamination reaction was not clear under the conditions examined. The amino acid mixture promoted cell growth accompanied by a marked increase in the amount of inosine produced. The AICA and some purine compounds stimulated the production slightly but far less than the amino acid mixture.