Quinone methides—and not dehydrodopamine derivatives—as reactive intermediates of β‐sclerotization in the puparia of flesh fly Sarcophaga bullata

Abstract

AbstractCuticular phenoloxidase(s) from Sarcophaga bullata larvae oxidized a variety of o‐diphenolic compounds. While catechol, 3,4‐dihydroxybenzoic acid, dopa, dopamine, and norepinephrine were converted to their corresponding quinone derivatives, other catechols such as 3,4‐dihydroxyphenylacetic acid, 3,4‐dihydroxyphenethyl alcohol, 3,4‐dihydroxyphenyl glycol, 3,4‐dihy‐droxymandelic acid, and N‐acetyldopamine were oxidized to their side‐chain oxygenated products. In addition, the enzyme‐catalyzed oxidation of the latter group of compounds accompanied the formation of colorless catecholcuticle adducts consistent with the operation of β‐sclerotization. Radioactive trapping experiments failed to support the participation of 1,2‐dehydro‐N‐acetyldopamine as a freely formed intermediate during phenoloxidase‐mediated oxidation of N‐acetyldopamine. When specifically tritiated substrates were provided, cuticular enzyme selectively removed tritium from [7‐3H]N‐acetyldopamine and not from either [8‐3H] or [ring‐3H]N‐acetyldopamine during the initial phase of oxidation. The above results are consistent with the generation and subsequent reactions of quinone methides as the initial products of enzyme‐catalyzed N‐acetyldopamine oxidation and confirm our hypothesis that quinone methides and not 1,2‐dehydro‐N‐acetyldopamine are the reactive intermediate of β‐sclerotization of sarcophagid cuticle. Quinone methide sclerotization resolves a number of conflicting observations made by previous workers in this field.