An enzyme exhibiting oxidase activity for beta-lactoglobulin, myoglobin, and L-lysine-containing peptides was found from a newly isolated fungal strain, Penicillium steckii AIU 027. The enzyme also oxidized L-amino acids, N-alpha-benzylox-ycarbonyl-L-lysine (N-alpha-Z-L-lysine) and N-epsilon-Z-L-lysine, but not D-amino acids and amines. Thus, the enzyme was classified into a group of L-amino acid oxidases (L-AAOs). However, characteristics of this L-AAO were significantly different from those of other L-AAOs as follows. The L-AAO from P. steckii AIU 027 oxidized both the a-amino group and the e-amino group in i.-amino acids and L-lysine-containing peptides, and the values for L-lysine-containing polypeptides were lower than those for N-alpha-Z-L-lysine and L-lysine-containing dipeptides. The enzyme contained flavin and iron, and composed of four identical subunits with molecular mass of 75.3 KDa. The N-terminal amino acid sequence, ENIAD-VADAMGPWFDGVAYMKSKKN, was different from that of other L-AAOs. Thus, the L-AAO with protein oxidase activity was first reported here from P. steckii AIU 027. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.