Abstract
The adenine-sparing action of amino acid mixture (Difco "casamino acid" type) for inosine formation by adenine- and adenine-histidine-requiring mutants of Bacillus subtilis was revealed to be brought about by a combination of the following L-amino acids contained in the original mixture: histidine plus mixture of eight amino acids, isoleucine, leucine, methionine, glycine, valine, threonine, phenylalanine and lysine. Histidine was demonstrated to be essential, but the mixture of the eight amino acids could be fully replaced by a suitable concentration of phenylalanine alone. Histidine alone could not display the sparing action, and in the same way, the mixture of the eight amino acids or phenylalanine could not exert this action in the absence of histidine. A fairly large amount of certain amino acids mentioned above was required for expression of the sparing action by histidine.
A minimal concentration of histidine for the sparing action with adenine-requiring mutant was about 7mg%, while a larger amount of it was required with adenine-histidine-requiring mutant. Inosine formation in 30mg% of adenine-added medium was strongly repressed by a large amount of amino acid mixture due to its adenine-sparing action, but the amount of 5-amino-4-imidazolecarboxamide riboside accumulated in this medium as a by-product, especially in the growing phase, was larger than that in the medium being suitable for inosine formation.
