Melanin biosynthesis inVerticillium dahliae: Dehydration and reduction reactions in cell-free homogenates

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Abstract

Cell-free homogenates and anaerobic conditions were used to study melanin biosynthesis in the imperfect fungusVerticillium dahliae Kleb. The homogenates reduced 1,3,6,8-tetrahydroxynaphthalene to scytalone and 1,3,8-trihydroxynaphthalene to vermelone. 1,3,6,8-Tetrahydroxynapthalene has not been isolated from fungi and was previously considered a hypothetical intermediate in the melanin pathway. This is the first report of its use as an exogenous melanin substrate. The enzymatic reductions required NADPH as a cofactor. The reactions were inhibited by the systemic fungicides tricyclazole (EL-291), pyroquilon (CGA-49104) and 4,5-dihydro-4-methyltetrazolo [1,5α]quinazolin-5-one (PP-389), and were eliminated by heating homogenates to 40°C for 35 minutes prior to the addition of substrate. The homogenates also enzymatically dehydrated scytalone to 1,3,8-trihydroxynaphthalene and vermelone to 1,8-dihydroxynaphthalene. The dehydration reactions did not require pyridine nucleotides, were insensitive to the systemic fungicides, and were eliminated after heating at 70°C for 35 minutes.

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