REGULATION OF L-ISOLEUCINE BIOSYNTHESIS IN THE PHOTOSYNTHETIC BACTERIUM RHODOSPIRILLUM RUBRUM

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Abstract
The cell-free biosynthetic threonine deaminase of R. rubrum superficially appears to be atypical in that inhibition of enzyme activity by L-isoleucine (observed at low L-threonine concentrations) is relieved by an increase of the substrate concentration. By appropriate treatment with papain, the deaminase can be modified to a form which shows significantly increased sensitivity to isoleucine. Isoleucine in-vivo, must be an effective regulator of threonine deaminase activity; a relevant re-interpretation of the integrated feedback controls concerned with regulating synthesis of isoleucine and other amino acids of the aspartic family pathway in R. rubrum is presented.