Abstract
A mutant, No. 1-231, resistant to S-P-aminoethyty-L-cysteine (AEC) plus threonine which was previously derived from a low citrate synthase mutant (No. 1 5-8) of Brevibacterium flavum, produced 41 g/liter of lysine (as HC1 salt, 41 %yield) and showed pyruvate kinase and homoserine dehydrogenase activities of about 1/10 and 1/20 as much as those of No. 15-8, respectively, but its aspartokinase was still normally sensitive to the feedback inhibition by lysine plus threonine. Another AEC-resistant mutant, No. 2-190, from No. 15-8 showed aspartokinase insensitive to the feedback inhibition without any change in pyruvate kinase and homoserine dehydrogenase activities. In addition, both the two AEC-resistant mutants and parent No. 1 5-8 showedpartial desensitization of phosphoenolpyruvate carboxylase to the feedback inhibition by L-aspartic acid. β-Fluoropyruvic acid-sensitive mutants No. 22 and No. 2-1 1 were derived from No. 1-231.These sensitive strains produced 51 g/liter of lysine (51 %yield) and were found to be completely defective in homoserine dehydrogenase activity. It was concluded from the results that depression of pyruvate kinase activity leads to an increase in lysine production.
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