Arginine Racemase of Pseudomonas graveolens: I. PURIFICATION, CRYSTALLIZATION, AND PROPERTIES

Abstract

Abstract Arginine racemase has been purified approximately 5400-fold and crystallized from an extract of Pseudomonas graveolens. The purification procedure consists of sonic disruption, ammonium sulfate fractionation, treatment with 1-butanol, DEAE-cellulose and DEAE-Sephadex column chromatography, and Sephadex G-150 gel filtration, followed by crystallization. The purified enzyme is homogeneous by the criteria of ultracentrifugation (s020,w = 5.2 S) and disc gel electrophoresis. The molecular weight is 167,000, assuming a partial specific volume of 0.74. The enzyme is yellow in solution and exhibits an absorption maximum at 420 mµ. The absorption spectrum is shifted neither by varying pH of the enzyme nor by addition of arginine. One mole of pyridoxal 5'-phosphate is tightly bound per 42,000 g of enzyme. The apoenzyme was obtained by dialysis against phenylhydrazine solution. Addition of pyridoxal 5'-phosphate caused return of the 420 mµ absorption peak and reconstitution of activity. Reduction of arginine racemase with sodium borohydride shifted the 420 mµ peak to about 315 mµ, and destroyed the racemase activity. The enzyme catalyzes racemization of lysine, arginine, e-N-acetyllysine, ornithine, 2,3-diaminopropionate, homoarginine, 2,4-diaminobutyrate, ethionine, citrulline, homocitrulline, δ-N-acetylornithine, theanine, glutamine, and methionine in this order, when examined at pH 10.0. Maximum activities for arginine, lysine, theanine, and ornithine are found in the pH regions of 9.0 to 10.6, 7.5 to 10.6, 7.0 to 10.0, and 6.5 to 9.0, respectively. The following Michaelis constants were determined: d-arginine, 1.0 x 10-3 m, and pyridoxal 5'-phosphate, 4.0 x 10-7 m. The enzyme activity was inhibited by hydroxylamine and d- and l-penicillamine.