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Appl Environ Microbiol. 1967 July; 15(4): 694-700
Copyright © 1967 American Society for Microbiology. All Rights Reserved.

Decarboxylation of -Keto Acids by Streptococcus lactis var. maltigenes¹

Department of Animal Industries, University of Connecticut, Storrs, Connecticut 06268

ABSTRACT

Decarboxylation rates for a series of C-3 to C-6 -keto acids were determined in the presence of resting cells and cell-free extracts of Streptococcus lactis var. maltigenes. The C-5 and C-6 acids branched at the penultimate carbon atom were converted most rapidly to the respective aldehydes in the manner described for -carboxylases. Pyruvate and -ketobutyrate did not behave as -carboxylase substrates, in that O₂ was absorbed when they were reacted with resting cells. The same effect with pyruvate was noted in a nonmalty S. lactis, accounting for CO₂ produced by some "homofermentative" streptococci. Mixed substrate reactions indicated that the same enzyme was responsible for decarboxylation of -ketoisocaproate and -ketoisovalerate, but it appeared unlikely that this enzyme was responsible for the decarboxylation of pyruvate. Ultrasonic disruption of cells of the malty culture resulted in an extract inactive for decarboxylation of pyruvate in the absence of ferricyanide. Dialyzed cell-free extracts were inactive against all keto acids and could not be reactivated.

² Present address: Chas. Pfizer & Co., Inc., Groton, Conn.

¹ Scientific Contribution No. 236, Agricultural Experiment Station, University of Connecticut, Storrs. This paper was prepared from data presented by the senior author in partial fulfillment of the requirements for the Ph.D. degree at the University of Connecticut.