N-Acetyl-6-hydroxytryptophan oxidase, a developmentally controlled phenol oxidase from Aspergillus nidulans

Abstract

We have purified a specific phenol oxidase which is produced during conidiophore development in the fungus AspergiZZus niduZms. Two active forms (A and B) have molecular masses of 50 and 48 kDa respectively; they have identical N-termini (24 residues). We have analysed the metal ion content of the B form; it is unusual in consisting of one zinc and two copper atoms per molecule. A temperature-sensitive mutant (ivoB192) produces a thermolabile enzyme, implying that ivoB is the structural locus. The natural substrate of the enzyme is N-acetyl-6-hydroxytryptophan, but it can be assayed colorimetrically or polarographically using hydroquinone monomethyl ether (HME) as substrate. It will also oxidize p-cresol, but not tyrosine, 3,4-dihydroxyphenylalanine or o-methoxyphenol. Colour development with HME substrate is strongly enhanced by high ammonium ion concentrations. Activity against HME is inhibited by 2,3-dihydroxynaphthalene, phenylhydrazine, diethyl dithiocarbamate and &hydroxyquinolene.

The genetics of conidiophore pigmentation in Aspergillus nidulans.

“…This procedure, and the colorimetric assay using hydroquinone monomethyl ether as substrate, are as described by Birse & Clutterbuck (1990~). In the medA/medA+ comparison 10 m~-phosphate buffer (pH 7.0) was substituted for ammonium tartrate.…”

Transcriptome changes initiated by carbon starvation in Aspergillus nidulans

“…Among them, the induction of ivoA and the gene AN0230 was confirmed by rRT-PCR (Table 2). Both ivoA and ivoB are involved in the Tyr-based melanin biosynthesis (Birse & Clutterbuck, 1990), while AN0230 (Nahlik, 2007) together with AN2091 encodes putative tyrosinases and is potentially also involved in this process. Although melanin formation was not detected at the 4 h incubation time, the formation of this pigment was visible in older cultures.…”

“…However, in older (24 h) cultures, conidiophore development was observed, although these conidiophores were underdeveloped, similarly to those observed by Skromne et al (1995), and peeled off easily from the pellets (data not shown). In contrast to abaA, the induction of several BrlA-dependent genes was observed, including rodA, which is responsible for the rodlet surface of conidia (Girardin et al, 1999), ivoA and ivoB, which play roles in melanin production and conidiophore pigmentation (Birse & Clutterbuck, 1990), and several genes encoding extracellular hydrolases (chiB, engA, prtA and pepJ) (Tables 2 and S2). Upregulation of genes involved in asexual development (including brlA, abaA, wetA and several hydrophobin genes) was also observable during the carbon starvation of A. niger (Nitsche et al, 2012).…”

Wild-type and mutant alleles of the Aspergillus nidulans developmental regulator gene brlA: correlation of variant sites with protein function

“…Martinelli), and G34 (yA2; methH2 argB2; veA1). Mycelia for DNA extraction were grown at 37°C for 30 h as surface cultures (Birse and Clutterbuck 1990).…”