Two Distinct Quinoprotein Amine Oxidases are Induced by n‐Butylamine in the Mycelia of Aspergillus niger AKU 3302

Abstract

Two distinct quinoprotein amine oxidases were found in Aspergillus niger mycelia grown on n‐buty‐lamine medium and purified using chromatographic techniques. The respective enzymes were termed AO‐I, which had already been isolated, and AO‐II, a new enzyme found in this study. HPLC indicated that their molecular masses are 150 kDa and 80kDa, respectively. On SDS/PAGE, the enzymes gave a similar but distinct mobility, which corresponds to 75 kDa for the subunit of dimeric AO‐I and 80 kDa for monomeric AO‐II. The absorption spectra of both enzymes were different from each other; the absorption maxima in the visible region were at 490 nm for AO‐I and 420 nm for AO‐II. The enzymes showed positive quinone staining, comparable substrate specificity, and sensitivity to inhibitors typical for copper/ topa quinone‐containing amine oxidases, but they had different copper contents and also differed in their N‐terminal sequences. Their peptide maps showed almost identical patterns, with the exception of two additional bands for AO‐II. Among the peptides obtained from digestion of AO‐II, peptides with sequences corresponding to the N‐terminal part of AO‐I were detected. Polyclonal antibodies raised against AO‐I and AO‐II recognized both enzymes, but with different specificities. Using precipitation with AO‐I, the antibody prepared against AO‐II was purified and was shown to be specific only for AO‐II. The cDNA of AO‐I was cloned and sequenced. A highly conserved tetrapeptide sequence, Asn‐Tyr‐Glu‐Tyr, was identified in which the first tyrosine residue (Tyr404) that could be converted to topa quinone was present in the 670‐residue deduced amino acid sequence. Northern blot analysis indicated that AO‐I was highly expressed in A. niger grown on n‐butylamine as a single nitrogen source. Genomic Southern blot analysis confirmed that both enzymes are likely to be encoded by the same gene.