SUMMARY: Isoleucine increased the quantity of α-acetolactic acid-forming enzyme which takes part in the synthesis of valine and isoleucine in . Threonine and α-ketobutyric acid, the precursors of isoleucine, had a similar effect. In during the initial stage of growth after inoculation, a temporary substantial increase of α-acetolactic acid-forming enzyme can be observed. This increase was not so great when valine was present, and was enhanced by isoleucine, which was effective during the whole period of growth. The repressive effect of valine can be counteracted with isoleucine and the end product inductive effect of isoleucine can be inhibited by valine. In extracts of disrupted organisms the activity of the α,β-dihydroxy acid dehydrase changes parallel with the concentration of the α-acetolactic acid-forming enzyme.

In the case of the repressive effect of valine on the α-acetolactic acid-forming enzyme can be counteracted with isoleucine.


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