The enzymic activation of d-alanine

Abstract

An amino acid-activating enzyme for D-alanine was detected in Lactobacillus arabinosus, L. casei, Bacillus subtilis and Staphy-lococcus aureus H. It has been purified 25-fold from ultrasonic extracts of acetone-dried cells of L. arabinosus. The enzyme catalyzes a[P32] pyro-phosphate-adenosine triphosphate (ATP) exchange in the presence of D-alanine and Mg2+ ions and the formation of D-alanine hydroxamate in the presence of ATP, Mg2+ ions, hydroxylamine and D-alanine. These reactions are consistent with the formation of an adenosine monophosphate[long dash]D-alanine anhydride in combination with the enzyme. In the [P32] pyrophos -phate[long dash]ATP exchange the Km for D-alanine is 70 mM, and for inorganic pyrophosphate it is 0.13 mM. The concentration of ATP required for one-half maximal velocity is 2.5 mM. The purified enzyme preparation is specific for D-amino acids. In addition to D-alanine this preparation catalyses a small but significant [p32]-pyrophosphate[long dash]ATP exchange in the presence of D-a-amino-n-butyric acid (14.6%) and D-serine (7.5%). The properties of this enzyme were compared with those of other amino acid-activating enzymes and its possible significance in the biosynthesis of bacterial cell-wall components is discussed.