Regulation of Alanine Dehydrogenase in Bacillus licheniformis

Abstract

Cell extracts of Bacillus licheniformis were found to contain nicotinamide adenine dinucleotide (NAD)-dependent l -alanine dehydrogenase (ADH) ( l -alanine: NAD oxidoreductase, EC 1.4.1.1). High specific activities (3.5 to 6.0 IU/mg of protein) were found in extracts of cells throughout growth cycles only when l -alanine served as the primary source of carbon or carbon and nitrogen. Specific activities were minimal (0.02 to 0.04 IU/mg of protein) during growth on glucose, but increased at least sevenfold during the first 5 h of postlogarithmic-phase metabolism. Addition of 10 mM glucose to cultures during logarithmic-phase growth on l -alanine resulted in a rapid decrease in enzyme activity. Addition of 20 mM l -alanine to cells near the completion of log-phase growth on glucose resulted in a 20-fold increase in ADH specific activity during less than one cell generation. Extracts of postlogarithmic-phase cells cultured on glucose, malate, l -glutamate, or Casamino Acids contained intermediate levels of ADH activity. The enzyme was partially purified from crude extracts of B. licheniformis , and apparent kinetic constants were estimated. A role for ADH in the catabolism of l -alanine to pyruvate during vegetative growth on l -alanine and during sporulation of cells cultured on glucose is proposed on the basis of these experimental results.