Crystalline Mammalian l-Amino Acid Oxidase from Rat Kidney Mitochondria

l -Amino acid oxidase has been crystallized from extracts of rat kidney mitochondria. Purification involved sonic extraction, ammonium sulfate fractionation, chromatography on diethylaminoethyl cellulose, and gel filtration through Sephadex G-200. The enzyme revealed a single protein band on starch gel electrophoresis and exhibited a single homogeneous peak ( s 20, w 0 = 10.5 S) in an ultracentrifuge. The enzyme is a flavoprotein in which the prosthetic group appears to be flavin mononucleotide. On the basis of the flavin mononucleotide content of the enzyme (0.92%) and its molecular weight (88,900 ± 1,100), it has been concluded that the enzyme contains 2 moles of flavin mononucleotide per mole. The enzyme catalyzes the oxidation of many α-aminomonocarboxylic and α-hydroxy acids ( l configuration) but has no action on optically inactive acids such as glycine and α-hydroxyisobutyric acid. The turnover numbers for the oxidation of l -leucine and of l -lactic acid were 6.3 and 26 moles per min per mole of flavin mononucleotide conjugated with enzyme, respectively.