Expression of D-amino acid oxidase in Rhodotorula gracilis under induction conditions: a biochemical and cytochemical study.

D-amino acid oxidase is expressed to a high level in the yeast Rhodotorula gracilis (0.3% of total cell protein) through induction by D-alanine in a defined growth medium. Monospecific polyclonal antibodies against pure enzyme were obtained. Western blot analysis showed that the enzyme is synthesized as the mature polypeptide. The localization of the enzyme was investigated by immunoelectron microscopy using the postembedding immunogold technique and by submicroscopic enzyme cytochemistry. D-Amino acid oxidase was detected in peroxisomes, and quantitation of immunoelectron microscopic data indicated that the enzyme is exclusively confined to these organelles. Immunoelectron microscopic observations are in complete agreement with biochemical data showing that the enzyme is not expressed in the absence of D-alanine. Morphometric analysis demonstrated that induction of D-amino acid oxidase synthesis is associated with a 241% increase of peroxisome volume density and with a 31% increase of peroxisome size as compared to cells grown on non-inducing medium.