Distribution and immunochemical properties of rat kidney L-amino-acid oxidase, with a note on peroxisomes

Substrate specificity of human glutamine transaminase K as an aminotransferase and as a cysteine S-conjugate beta-lyase

Rat kidney glutamine transaminase K (GTK) exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate beta-lyase. The beta-lyase reaction products are pyruvate, ammonium and a sulfhydryl-containing fragment. We show here that recombinant human GTK (rhGTK) also exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate beta-lyase. S-(1,1,2,2-Tetrafluoroethyl)-l-cysteine is an excellent aminotransferase and beta-lyase substrate of rhGTK. Moderate aminotransferase and beta-lyase activities occur with the chemopreventive agent Se-methyl-l-selenocysteine. l-3-(2-Naphthyl)alanine, l-3-(1-naphthyl)alanine, 5-S-l-cysteinyldopamine and 5-S-l-cysteinyl-l-DOPA are measurable aminotransferase substrates, indicating that the active site can accommodate large aromatic amino acids. The alpha-keto acids generated by transamination/l-amino acid oxidase activity of the two catechol cysteine S-conjugates are unstable. A slow rhGTK-catalyzed beta-elimination reaction, as measured by pyruvate formation, was demonstrated with 5-S-l-cysteinyldopamine, but not with 5-S-l-cysteinyl-l-DOPA. The importance of transamination, oxidation and beta-elimination reactions involving 5-S-l-cysteinyldopamine, 5-S-l-cysteinyl-l-DOPA and Se-methyl-l-selenocysteine in human tissues and their biological relevance are discussed.

IL-4-Induced Gene-1 Is a Leukocyte l-Amino Acid Oxidase with an Unusual Acidic pH Preference and Lysosomal Localization

IL-4-induced gene-1 (Il4i1 or Fig1) initially isolated as a gene of unknown function from mouse B lymphocytes, is limited in expression to primarily immune tissues and genetically maps to a region of susceptibility to autoimmune disease. The predicted Il4i1 protein (IL4I1) sequence is most similar to apoptosis-inducing protein and Apoxin I, both l-amino acid oxidases (LAAO; Enzyme Commission 1.4.3.2). We demonstrate that IL4I1 has unique LAAO properties. IL4I1 has preference for aromatic amino acid substrates, having highest specific activity with phenylalanine. In support of this selectivity, IL4I1 is inhibited by aromatic competitors (benzoic acid and para-aminobenzoic acid), but not by nonaromatic LAAO inhibitors. Il4i1 protein and enzyme activity is found in the insoluble fraction of transient transfections, implying an association with cell membrane and possibly intracellular organelles. Indeed, IL4I1 has the unique property of being most active at acidic pH (pH 4), suggesting it may reside preferentially in lysosomes. IL4I1 is N-linked glycosylated, a requirement for lysosomal localization. Confocal microscopy of cells expressing IL4I1 translationally fused to red fluorescent protein demonstrated that IL4I1 colocalized with GFP targeted to lysosomes and with acriflavine, a green fluorescent dye that is taken up into lysosomes. Thus, IL4I1 is a unique mammalian LAAO targeted to lysosomes, an important subcellular compartment involved in Ag processing.

Peroxisomal oxidation of L-2-hydroxyphytanic acid in rat kidney cortex

A previously unreported metabolite of mammalian phytanic acid catabolism, 2-oxophytanic acid, was identified by gas chromatography/mass spectrometry analysis. The formation of 2-oxophytanic acid was demonstrated to result from the oxidation of L-2-hydroxyphytanic acid, a reaction catalysed by a rat-kidney-cortex H2O2-generating oxidase. The pH optimum for the L-2-hydroxyphytanate oxidase activity was 8.5 and its apparent Km and Vm were about 0.15 mM and 0.35 mumol min-1 (g tissue)-1, respectively. L-2-Hydroxyisocaproate, a substrate of rat kidney L-alpha-hydroxyacid oxidase type B, inhibited the formation of 2-oxophytanate from L-2-hydroxyphytanic acid. Fractionation studies have indicated that 40% of L-2-hydroxyphytanate oxidase was associated with a particulate fraction and that the activity distribution of the oxidase closely paralleled that of catalase, a well known peroxisomal marker enzyme.

Amino acid oxidase of leukocytes in relation to H 2 O 2 -mediated bacterial killing

D-Amino acid oxidase and L-amino acid oxidase have been measured in sucrose homogenates of polymorphonuclear leukocytes (PMN) obtained from guinea pigs and humans. Subcellular distribution patterns and studies on latency indicate that these oxidases are soluble enzymes. Their hydrogen peroxide-generating capacity was verified. Chronic granulomatous disease PMN, which lack a respiratory burst and fail to generate H(2)O(2) during phagocytosis and do not kill catalase positive bacteria, had peroxide-generating amino acid oxidase activity equal to that found in PMN homogenates from patients with bacterial infections. The precise metabolic and bactericidal role of amino acid oxidases in PMN remains uncertain.