Open AccessN-Acetyl-6-hydroxytryptophan oxidase, a developmentally controlled phenol oxidase from Aspergillus nidulans
Author(s) -
C E Birse,
A. J. Clutterbuck
Publication year - 1990
Publication title -
journal of general microbiology/journal of general microbiology
Language(s) - English
Resource type - Journals
eISSN - 2059-9323
pISSN - 0022-1287
DOI - 10.1099/00221287-136-9-1725
Subject(s) - chemistry , flavin group , aspergillus nidulans , hydroquinone , enzyme , thermolabile , substrate (aquarium) , choline oxidase , oxidase test , monoamine oxidase , tyramine , stereochemistry , organic chemistry , biochemistry , mutant , acetylcholinesterase , gene , oceanography , geology
We have purified a specific phenol oxidase which is produced during conidiophore development in the fungus Aspergillus nidulans. 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 8-hydroxyquinolene.