The Journal of General Physiology
Cell MicroControls
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The Journal of General Physiology, Vol 34, 211-224, Copyright © 1950 by The Rockefeller University Press

ARTICLE

REGULATORY MECHANISMS OF CELLULAR RESPIRATION

III. ENZYME DISTRIBUTION IN THE CELL. ITS INFLUENCE ON THE METABOLISM OF PYRUVIC ACID BY BAKERS' YEAST



E. S. Guzman Barron 1, Maria Isabel Ardao 1, and Marion Hearon 1

1 From the Chemical Division, Department of Medicine of The University of Chicago, Chicago

The rate of the aerobic metabolism of pyruvic acid by bakers' yeast cells is determined mainly by the amount of undissociated acid present. As a consequence, the greatest rate of oxidation was observed at pH 2.8. Oxidation, at a slow rate, started at pH 1.08; at pH 9.4 there was no oxidation at all. The anaerobic metabolism, only a fraction of the aerobic, was observed only in acid solutions. There was none at pH values higher than 3.

Pyruvic acid in the presence of oxygen was oxidized directly to acetic acid; in the absence of oxygen it was metabolized mainly by dismutation to lactic and acetic acids, and CO2. Acetic acid formation was demonstrated on oxidation of pyruvic acid at pH 1.91, and on addition of fluoroacetic acid. Succinic acid formation was shown by addition of malonic acid. These metabolic pathways in a cell so rich in carboxylase may be explained by the arrangement of enzymes within the cell, so that carboxylase is at the center, while pyruvic acid oxidase is located at the periphery.

Succinic and citric acids were oxidized only in acid solutions up to pH 4. Malic and alpha-ketoglutaric acids were not oxidized, undoubtedly because of lack of penetration.

Submitted on June 23, 1950


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