ISOLEUCINE AND VALINE METABOLISM IN ESCHERICHIA COLI V

Publisher Website
Google Scholar
Abstract
Two kinds of antagonism between isoleucine and valine in Escherichia coli were studied. One, in which valine inhibits and isoleucine reverses, was observed in wild type strain K-12 and an isoleucineless mutant which can utilize the 4-C precursors for isoleucine synthesis. Isoleucineless mutants, blocked later in the pathway and requiring one of the 6-C precursors of isoleucine, are insensitive to valine. On the basis of this and other evidence it is concluded that isoleucine reverses the inhibition of valine non-competitively and that valine blocks the synthesis of an early 6-C precursor of isoleucine. The other antagonism is one in which excess isoleucine inhibits the utilization of valine by mutants requiring both isoleucine and valine. This inhibition can be by-passed by substituting peptides of valine for free valine. Isoleucine apparently acts at the cell surface by preventing the permeation of valine.