Abstract
Under the shift-down condition, threonine, α-ketobutyrate and isoleucine at certain concentrations derepressed the synthesis of acetohydroxy acid synthase and isomeroreductase but did not derepress that of transaminase B or threonine deaminase in Escherichia coli W3110-215.
Leucine and/or valine counteracted the derepressing effect of isoleucine on the synthesis of acetohydroxy acid synthase and isomeroreductase. Leucine and valine in the absence of isoleucine completely inhibited derepression of the synthesis of these enzymes after shift-down. These results suggested that isoleucine at a certain concentration is possibly necessary for the efficient derepression of the synthesis of acetohydroxy acid synthase I coded by the ilvB gene and/or acetohydroxy acid synthase III coded by the ilvHI gene.
