Enzymes of the Isoleucine-Valine Pathway in Acinetobacter

Abstract

Regulation of four of the enzymes required for isoleucine and valine biosynthesis in Acinetobacter was studied. A threeto fourfold derepression of acetohydroxyacid synthetase was routinely observed in two different wild-type strains when grown in minimal medium relative to cells grown in minimal medium supplemented with leucine, valine, and isoleucine. A similar degree of synthetase derepression was observed in appropriately grown isoleucine or leucine auxotrophs. No significant derepression of threonine deaminaseor transaminase B occurred in either wild-type or mutant cells grown under a variety of conditions. Three amino acid analogues were tested with wild-type cells; except for a two-to threefold derepression of dihydroxyacid dehydrase when high concentrations of aminobutyric acid were added to the medium, essentially the same results were obtained. Experiments showed that threonine deaminase is subject to feedback inhibition by isoleucine and that valine reverses this inhibition. Cooperative effects in threonine deaminase were demonstrated with crude extracts. The data indicate that the synthesis of isoleucine and valine in Acinetobacter is regulated by repression control of acetohydroxyacid synthetase and feedback inhibition of threonine deaminase and acetohydroxyacid synthetase.

Pyrimidine Metabolism in Acinetobacter calcoaceticus

“…This is a widely occuring species which differs from E. coli in many respects (22). A number of reports have appeared in the last years both on metabolism (23,24) and taxonomy (1,9,29,22) of this species.…”

Preparations and properties of ribonucleic acid polymerase from Acinetobacter calcoaceticus

“…We have recently described some aspects of DNA synthesis in the bacterium Acinetobacter calcoaceticus (21,22). A number of reports have also recently appeared on the physiology, metabolism, and taxonomy of this organism (2,15,25,(28)(29)(30)(31). The pyrimidine metabolism is quite different from that of Escherichia coli (22), and it resembles that of Neisseria meningitidis (16,17); both organisms are incapable of incorporating exogenous thymine or thymidine into their DNA.…”