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The Conversion of Alpha-Ketoisovaleric Acid to Valine by Lactic Streptococci¹

Dept. of Animal Industries, Storrs Agricultural Experiment Station, University of Connecticut, Storrs

ABSTRACT

Streptococcus lactis, Streptococcus cremoris, and Streptococcus lactis var. maltigenes require valine for multiplication (1, 4, 7). The malty variant of S. lactis has been shown, in addition, to convert valine to 2-methylpropanal (6). If the degradation of valine follows a pattern similar to that of leucine by cells of S. lactis and its variant (4), then alpha-ketoisovaleric acid should fill the valine requirement of these organisms when substituted for the amino acid in a completely defined medium, and the formation of valine from its alpha-ketoacid analog should be demonstrable.

The methods followed to demonstrate the above precepts were similar to those described in an earlier publication (4).

The basal synthetic medium used was that of Niven (7), modified as follows: (a) the proportions of the amino acids found in casein (3) were substituted at levels comparable to those in casein hydrolyzate; and (b), sodium acetate was added to the medium as recommended by Collins et al. (2).

¹ This investigation was supported in part by U.S.P.H.S. research grant (E-2711-A) from the National Institute of Allergy and Infectious Diseases, Department of Health, Education and Welfare, Public Health Service.