Absence of Laccase from Yellow-spored Mutants of Aspergillus nidulans

Abstract

SUMMARY Green-spored strains of Aspergillus nidulans contain a p-diphenol oxidase (laccase) which is only formed during sporulation and is absent from yellow-spored mutants. The enzyme was assayed colorimetrically using N,N-dimethyl-p-phenyl- enediamine as substrate. Other substrates oxidized were pyrogallol, gallic acid and 2,6-dimethoxyphenol. Quinol, catechol and p-cresol were not detectably oxidized. Experiments with a temperature-sensitive yellow-spored mutant showed that the yA locus of A. nidulans is a structural gene for at least a component of the enzyme, while indirect evidence suggests that the enzyme also contains copper. Yellow-green- spored mutants of the ygA locus produce an inactive enzyme whose activity can be restored by dialysis against copper salts. Under certain conditions the enzyme itself can diffuse from a wild-type colony to a yellow-spored mutant colony and there act to give green spore pigment. From this it is deduced that the normal site of action of the enzyme may be external to the cell membrane. A similar enzyme has also been found in conidiating cultures of Aspergillus niger and Penicillium brevicompactum.