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Appl Environ Microbiol. 1974 August; 28(2): 265-270
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Insensitivity of Homocitrate Synthase in Extracts of Penicillium chyrosogenum to Feedback Inhibition by Lysine1

Prakash S. Masurekar2 and Arnold L. Demain

Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

ABSTRACT

We previously reported that lysine inhibits in vivo homocitrate synthesis in the lysine bradytroph, Penicillium chrysogenum L1, and that such feedback inhibition could explain the known lysine inhibition of penicillin formation. In the present study, it was found that dialyzed cell-free extracts of mutant L1 converted [1-14C]acetate to homocitrate. This homocitrate synthase activity was extremely labile but could be stabilized by high salt concentrations. The pH optimum of the reaction was 6.9, and the Km was 5.5 mM with respect to {alpha}-ketoglutarate. The reaction was also dependent upon the presence of Mg2+, adenosine 5'-triphosphate, and coenzyme A. Surprisingly, the activity in these crude extracts was not inhibited by lysine. Benzylpenicillin at a high concentration (20 mM) partially inhibited the enzyme, an effect that was enhanced by lysine. Casein hydrolysate also partially inhibited the enzyme.

FOOTNOTES

2 Present address: Research Laboratories, Eastman Kodak Company, Rochester, N.Y. 14650.

1 Contribution no. 2322 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Mass. 02139.

Appl Environ Microbiol. 1974 August; 28(2): 265-270
Copyright © 1974 American Society for Microbiology. All Rights Reserved.





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