THE PGR1 MUTANT OF COCHLIOBOLUS-HETEROSTROPHUS LACKS A P-DIPHENOL OXIDASE INVOLVED IN NAPHTHALENEDIOL MELANIN SYNTHESIS

1,8-Dihydroxynaphthalene (1,8-DHN) was isolated from Cochliobolus heterostrophus pale green mutant M13BL19 (Alb1+ Brn1+ Sal1+ Pgr1-1) as the active substance which restored melanization of HE1AS73 (Alb1-8 Brn1-2 Sal1-1 Pgr1+). HE1AS73 oxidized 1,8-DHN, 1-naphthol, N,N-dimethyl-p-phenylenediamine, tetramethylbenzidine, syringaldazine, and 3-(3,4-dihydroxyphenyl)alanine, but did not oxidize p-cresol and L-tyrosine. None of these compounds was oxidized by HE5R13 (Alb1-8 Brn1-2 Sal1-1 Pgr1-1). The syringaldazine oxidation activity of HE1AS73 was inhibited by diethyldithiocarbamate, cetyltrimethylammonium bromide, and dithiopyrimidine. These results indicate that the Pgr1+ strain contained p-diphenol oxidase which was absent from the Pgr1- strain. We consider from these results that p-diphenol oxidase, in which Pgr1 is involved, plays a role in melanin synthesis of C. heterostrophus and 1,8-DHN is a natural substrate of this enzyme.