Abstract
Metarhizium anisopliae produced an extracellular phenoloxidase and pigments in agar media containing catechol, methylcatechol, methylhydroquinone, or pyrogallol. Production of the enzyme and consequently of the pigment was favored by growth-limiting conditions. Phenoloxidase was not produced on agar containing l-dihydroxyphenylalanine (DOPA) unless growth was inhibited by capric acid or catechol. The black polyphenolic pigment resulting from growth on catechol resembled melanin in being oxidizable by H 2O 2 and soluble in solutions of NaOH but not HCl, but, in contrast to melanin, soluble in water and organic solvents. The enzyme ( pH optimum 7.5, pI < 3) showed a specificity for tyrosinase substrates (DOPA, dopamine, catechol, methyl catechol). Specific substrates for laccase (α-naphthol and 2,6-dimethoxyphenol) were not oxidized. Inhibitor studies suggested the enzyme contained copper and an O 2-binding site. Extraction of melanizing cuticles from M. anisopliae-infected Manduca sexta revealed only the insect tyrosinase ( pI ≈ 6). This and a histochemical study confirm that the fungal enzyme is not produced in situ during infection of M. sexta.
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