Possible role of a peroxidative system in melanin synthesis inVerticillium

Abstract

Manometric tests demonstrated phenolase activity in potato and mushroom extracts but little in extracts from a microsclerotial isolate ofVerticillium albo-atrum. The purpurogallin test indicated the presence of peroxidase activity in theseVerticillium extracts. An assay for an enzyme system which produced dark pigment from catechol was developed. Mn⁺⁺ stimulated pigment synthesis about twice as much as Mg⁺⁺ or Ca⁺⁺. Other cations, Co⁺⁺, Ni⁺⁺, Zn⁺⁺, Cu⁺⁺ and Fe⁺⁺ had less effect. The cell-free enzyme system containing H₂O₂ and Mn⁺⁺ produced dark-colored products from catechol, dopa, andp-phenylenediamine. Pyrogallol yielded a bright yellow color. Chemicals which did not yield colored products as a result of enzyme action included aniline, ascorbic acid, chlorogenic acid,p-cresol, gallic acid, hydroquinone, phenol, phenylalanine, protocatechuic acid, resorcinol, shikimic acid, and tyrosine. In view of these results and the failure of others to demonstrate more than weak phenolase activity inVerticillium, we conclude that a peroxidation probably initiates most melanin synthesis inVerticillium.