Regulation of phenylalanine oxidase synthesis in Proteus mirabilis

Cells of Proteus mirabilis could oxidize L-phenylalanine to phenylpyruvate only when grown in the presence of a number of amino acids, particularly, L-alanine, L-asparagine, L-glutamate, and L-glutamine. Production of phenylalanine oxidase was slowly lost upon growth in a minimal medium containing ammonium ions as a nitrogen source but was reversed by the addition of casein hydrolysate. Oxidase activity as well as a phenylalanine-dichlorophenolindophenol (DCIP) reductase activity increased in P. mirabilis only during cell multiplication. Both rifampin and nalidixic acid caused inhibition of oxidase synthesis. A phenylalanine-active transport was found to be operative when bacteria were grown in the absence of added amino acids. After anaerobic growth, cells of P. mirabilis had lost their ability to carry the phenylalanine oxidase reaction when assayed in the presence of air, and nitrate could not be used as an electron acceptor for the oxidation of phenylalanine. However, some phenylalanine-dichlorophenolindophenol reductase activity was still present in anaerobic bacteria at the early stage of cell multiplication.