We isolated Aspergillus carbonarius MU 205 as a new producer of an enzyme catalyzing oxidative deamination of 4-aminobutanamide (4-ABAD) to 4-oxobutanamide with the subsequent release of ammonia and hydrogen peroxide. Since the strain produced three enzymes with different K-m values for 4-ABAD, the enzyme with lowest K-m value (0.31 mM) was purified and revealed certain remarkable properties. The enzyme also oxidized aliphatic monoamines, aromatic amines and aliphatic aminoalcohols, but did not oxidize L-amino acids and aliphatic diamines. The V-max/K-m values for aliphatic monoamines were higher than that for 4-ABAD, and the enzyme activity was strongly inhibited by inhibitors of copper-containing amine oxidases. Thus, it was concluded that the enzyme might belong to a group of copper-containing amine oxidase. The 4-ABAD oxidase activity of this enzyme was optimum at pH 7.0, and the enzyme activity at pH 6.0 was 65% of that at pH 7.0. The enzyme was useful for increasing the sensitivity of L-lysine assay using L-amino acid oxidase/monooxygenase from Pseudomonas sp. AIU 813. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.