End-product Control of Acetohydroxyacid Synthetase by Valine in Penicillium chrysogenum Q176 and a High Penicillin-yielding Mutant

SUMMARY: Acetohydroxyacid synthetase produced by Penicillium chrysogenum q 176 and a high penicillin-producing mutant have been compared. Both were sensitive to valine as the major feedback inhibitor. Inhibition of the enzyme in q 176 appears to be effected through two valine binding sites, but only one of these remains in the high yielding strain and it is non-competitive with respect to pyruvate. The amount of enzyme activity detectable in the high yielding strain is more than twice the level in q 176. Control of acetohydroxy-acid synthetase by other related amino acids was shown to be complex and involved sites other than the valine binding site.