Valine-isoleucine Metabolism in Acetobacter Suboxydans and the Inhibition of Growth by Valine.

Kerwar, Suresh S. (Oregon State University, Corvallis), Vernon, H. Cheldelin, and L. W. Parks. Valine-isoleucine metabolism in Acetobacter suboxydans and the inhibition of growth by valine. J. Bacteriol. 88:179-186. 1964.-Extracts of Acetobacter suboxydans can synthesize valine and isoleucine via acetolactate and acetohydroxybutyrate, respectively. The amounts of these amino acids synthesized from different intermediates were determined. The pathways appear to be identical to those described for yeast, Neurospora, and Escherichia coli. When exogenous valine was added to a synthetic growth medium inoculated with A. suboxydans, no growth of the culture was observed. The inhibitory effect of valine was reversed by the addition of isoleucine. The site and mechanism of valine inhibition were investigated. Threonine deaminase was inhibited by valine and isoleucine but not by leucine. Repression of the deaminase by isoleucine but not by valine was indicated. The data reported in this paper suggest that valine prevented growth of the organism through false feedback inhibition of threonine deaminase, thereby limiting isoleucine biosynthesis.