SUBSTRATE-SPECIFICITY OF LENTIL SEEDLING AMINE OXIDASE

Copper diamine oxidase from lentil (Lens culinaris) seedlings was show n to be able to catalyze the oxidative deamination of a wide range of aliphatic and aromatic monoamine compounds, including some amino acids . Although the catalytic efficiencies were only 1-3% of that measured with the diamine substrate putrescine, they were still comparable to t hose of specialized monoamine oxidases. In particular, the lentil enzy me oxidized benzylamine and histamine with K-m and V-max values simila r to those found for the mammalian enzymes benzylamine oxidase and his taminase. Cysteamine was found to be a substrate of the enzyme, wherea s hypotaurine and taurine were found to be neither substrates nor inhi bitors of the enzyme. Quite unexpectedly the aminoacids L-ornithine an d L-lysine were oxidized by lentil enzyme, and beta-alanine and gamma- aminobutyric acid were oxidized only at high concentrations of enzyme. These results suggest that enzymes normally classified as diamine oxi dases could in fact have a more diversified role in metabolism than re cognized so far.