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J Bacteriol. 1972 October; 112(1): 251-258
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Concerted Feedback Inhibition of the Aspartokinase of Rhodospirillum tenue by Threonine and Methionine: a Novel Pattern

Malka Robert-Gero1, Lucien Le Borgne and Georges N. Cohen

a Laboratoire de Cytophysiologie de la Photosynthèse, C.N.R.S., 91—Gif-sur-Yvette, France, and Service de Biochimie cellulaire, Institut Pasteur, Paris, France

ABSTRACT

The presence of a single aspartokinase was demonstrated in Rhodospirillum tenue. The enzyme has been purified about 60-fold. No physical association exists in this species between aspartokinase and homoserine dehydrogenase. The general properties of the enzyme are described. Inhibition by L-lysine, by L-threonine, and concerted inhibition by these two end products are regulatory characters which have also been found in many other species. In R. tenue, aspartokinase is also subject to a hitherto not encountered type of concerted feedback inhibition, by L-threonine plus L-methionine. The inhibition caused by lysine can be reversed either by glycine, L-isoleucine, L-methionine, or L-phenylalanine. The concerted inhibition by lysine plus threonine is reversed by glycine, L-isoleucine, or L-phenylalanine, but not by L-methionine, which exerts in conjunction with threonine the independent concerted inhibition referred to above. Addition of single or several metabolites to cultures of R. tenue caused inhibition of growth and reversal of growth inhibition, compatible with the effects observed in vitro on aspartokinase activity. The regulation of this enzyme in relation to that of other bacterial aspartokinases is discussed.

FOOTNOTES

1 Present address: Laboratoire d'Enzymologie du C.N.R.S., 91—Gif-sur-Yvette, France.

J Bacteriol. 1972 October; 112(1): 251-258
Copyright © 1972 American Society for Microbiology. All Rights Reserved.





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