Abstract
This chapter discusses the methods of preparation of D -Amino Acid Dehydrogenase (Pseudomonas fluorescens). D -Amino acid dehydrogenases of Pseudomonas fluorescens catalyze the oxidation of D -amino acids in the presence of an appropriate hydrogen acceptor, liberating ammonia. Two distinct D -amino acid dehydrogenases, each showing absolute specificity for methylene blue or 2,6-dichloroindophenol, respectively, have been isolated. The methylene blue-specific D-amino acid dehydrogenase was detectable only in extracts from D -tryptophan-grown cells. The 2,6-dichloroindophenol- specific D -amino acid dehydrogenase is constitutive, being present in all cell extracts irrespective of culture conditions. D -Kynurenine was oxidized to kynurenic acid. Residual kynurenine was measured by the Bratton-Marshall procedure. A unit of enzyme was defined as the amount that caused the disappearance of 1 micromole of D -kynurenine per minute. Specific activity was expressed as units per milligram of protein. Under the conditions of the assay, the reaction rate was proportional to the amount of enzyme (up to 0.18 unit of enzyme) and the reaction rates were linear with time during the periods employed.
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