Induction of D-Amino-acid Oxidase by D-Alanine in Rhodotorula gracilis Grown in Defined Medium

Abstract

The obligate aerobe yeast Rhodotorula gracilis was grown in batch culture on a chemically defined, pH-controlled medium containing glucose or d-alanine as carbon sources, ammonium or d-alanine as nitrogen sources, and d-alanine as a sole carbon and nitrogen source. Under these conditions, d-alanine induced the synthesis of d-amino-acid oxidase (EC 1.4.3.3) to an extent depending on the nutrients, the highest specific activity of the enzyme [up to 0·6 U (mg protein)−1] being detected when both d-alanine and glucose were present in the growth medium. In contrast, enzyme activity was negligible when both ammonium and glucose were present in the growth medium, even in the presence of d-alanine. The racemic mixture dl-alanine was also utilized as a source of both carbon and nitrogen for the growth of R. gracilis, but the enzyme activity appeared only after the depletion of l-alanine from the medium. Data on transmembrane transport of d-alanine in the presence of different nutrients clearly indicated that the l-isomer prevented induction by d-alanine through inhibition of the transport of the d-amino acid into cells. However, such an effect was not exerted by ammonium, indicating that this compound probably acts at the level of enzyme synthesis.