D-amino acid dehydrogenases of Pseudomonas fluorescens.

Two distinct D-amino acid dehydrogenases, each showing absolute speci&ity for methylene blue or 2,6-dichloroindophenol, respectively, were isolated from Pseudomonas @orescens (ATCC 11299B). The methylene blue-specific ~-amino acid dehydrogenase was detectable only in extracts from D-tryptophan-grown cells and was purified about 40-fold. The 2,6-dichloroindophenol-specif?c ~-amino acid dehydrogenase is constitutive, being present in all cell extracts irrespective of culture conditions, and it was purified about G-fold. These enzymes appear to be flavoproteins in which the flavin adenine dinucleotide prosthetic group is tightly bound to the enzyme protein. The optimal pH of two enzymes was 7 to 8 and the Michaelis-Menten constant was 3 to 5 x low4 M for each Damino acid. Substrate specificity and thermal stability were observed to be somewhat different for the two enzymes. No inhibition of these enzymes was observed with metal chelating agents.