STUDIES ON THE METABOLISM OF MYCOBACTERIUM TUBERCULOSIS VII

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Abstract
Lactic, pyruvic, acetic, fumaric, malic, succinic, citric, oxalacetic, and alpha-ketoglu-taric acids were oxidized by cell-free extracts of the avirulent H37Ra strain of Mycobacterium tuberculosis var. hominis. A centrifugal fractionation procedure produced a twofold increase in enzymatic activity for lactate and citrate. C of. actors adenosine triphosphate, diphosphopyridine nucleotide, and coenzyme A increased the rate of oxygen uptake with all substrates except pyruvate and lactate. Plotting O2 uptake against time, linear curves for lactate, fumarate, and L-malate were obtained while with the remainder of the substrates, pyruvate, acetate, oxal-acetate, alpha-ketoglutarate, succinate, and citrate, curves which leveled off after 10 to 30 minutes were obtained. Storage of extracts at 5[degree] C for one week had no effect on enzymatic activity. Freezing at -20[degree] C for 20 days decreased endogenous and citrate dehydrogenase activities while it increased lactate dehydrogenase activity slightly. The fact that a hydrogen carrier, methylene blue, was required for lactate activity indicated that lactate oxidase was absent from H37Ra extracts. Citrate was synthesized from fumarate and malate by H37Ra extracts and was identified both chromatographically and chemically. Utilization of many Krebs'' cycle intermediates and their precursors and the synthesis of citrate indicate that the avirulent H37Ra strain of M. tuberculosis var. hominis possesses a citric acid terminal respiratory cycle.

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