Some properties of mandelate racemase from Pseudomonas fluorescens.

1. l-Mandelate dehydrogenase and mandelate racemase were partially purified from extracts of Pseudomonas fluorescens A-312 grown in media containing d-mandelate. 2. The activity of mandelate racemase, but not that of l-mandelate dehydrogenase, is greatly stimulated by Mg(2+), Mn(2+), Co(2+) and, though less effectively, by Ni(2+). Other metal ions are inactive or inhibitory. 3. Racemase activity is inhibited by phosphate, fluoride, pyrophosphate and EDTA. The inhibitions by pyrophosphate and EDTA are competitive with respect to the metal ion activator; those by phosphate and fluoride are competitive with respect to the substrate. 4. The addition of Mg(2+) diminishes the Michaelis constant of racemase. 5. The pH optimum of the racemase is at 7.8. The pH-activity curve of the dehydrogenase complex of enzymes has two peaks, at 7.0 and 8.2. 6. The enzymic racemization of d-mandelate is initially faster than that of l-mandelate. 7. The rates of oxidation of related substrates, catalysed by l-mandelate dehydrogenase, are in the decreasing order: l-p-hydroxymandelate; l-3,4-dihydroxymandelate; l-4-hydroxy-3-methoxymandelate. The racemase is active towards d-p-hydroxymandelate but inactive towards d-3,4-dihydroxymandelate and d-4-hydroxy-3-methoxymandelate. Since 4-hydroxy-3-methoxymandelate, and presumably also 3,4-dihydroxymandelate, arising from the metabolism of catechol-amines, have the d-configuration, the enzymes studied cannot be utilized for estimation of the last two acids in urine.