Guanosine Production and Purine Nucleotide Biosynthetic Enzymes in Guanosine-Producing Mutants of Bacillus subtilis

Abstract

Additions of methionine sulfoxide, psicofuranine and decoyinine resistances against an inosine-producing strain of Bacillus subtilis, 1411, were carried out successively. Finally, strain MG-1 that produced guanosine exclusively in a high yield was obtained. The correla-tions among these resistances, guanosine productivity, and regulatory mechanism of enzymes such as inosine 5'-monophosphate (IMP) dehydrogenase, guanosine 5'-monophosphate (GMP) synthetase, 5'-nucleotidase, phosphoribosylpyrophosphate (PRPP) amidotransferase and succino-adenosine 5'-monophosphate (succino-AMP) lyase were investigated.
Methionine sulfoxide resistance mainly caused decrease of specific activity of 5'-nucleoti-dase and partial losses of inhibition and repression of IMP dehydrogenase by GMP. Further-more, repression and inhibition of PRPP amidotransferase by GMP, and repression of succino-AMP lyase by GMP were also lost.
Psicofuranine resistance mainly caused variation of GMP synthetase, and partial loss of inhibition of succino-AMP lyase by AMP was observed.
Decoyinine resistance brought about complete losses of repression and inhibition of GMP synthetase by GMP, and loss of inhibition and partial loss of repression of succino-AMP lyase by AMP were also found.
From these results, it is concluded that the keys to increase guanosine production depend on losses of repression and feedback inhibition of IMP dehydrogenase, GMP synthetase, suc-cino-AMP lyase and PRPP amidotransferase, and further on degree of 5'-nucleotidase activity.