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On the nature of nonenzymatic and enzymatic oxidation of the putative sclerotizing precursor, 1,2‐dehydro‐N‐acetyldopamine
Author(s) -
Sugumaran Manickam,
Hennigan Brian,
Semensi Victor,
Dali Hemalata
Publication year - 1988
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.940080203
Subject(s) - chemistry , tyrosinase , dimer , enzyme , cuticle (hair) , stereochemistry , biochemistry , organic chemistry , biology , genetics
Abstract The mode of oxidation of 1,2‐dehydro‐N‐acetyldopamine by nonenzymatic and enzymatic systems was examined. At acidic and near neutral pH, this compound is fairly stable; however, even at slightly alkaline pH it is highly labile and undergoes spontaneous, nonenzymatic aerobic oxidation. Borate, which is known to chelate with catechols, prevented such nonenzymatic reaction, indicating the participation of the o ‐dihydroxyphenolic group in the oxidation process. The product of nonenzymatic oxidation was found to be not the expected o ‐benzoquinone derivative, but a benzodioxan‐type dimer. Although mushroom tyrosinase also catalyzed this reaction (Sugumaran et al.: Journal of Biological Chemistry 262 :10546–10549, 1987), cuticular phenoloxidase(s) from Sarcophaga bullata failed to mediate this conversion. Rather, the cuticular phenoloxidase(s) oxidized the parent compound to a reactive intermediate which got bound to cuticle irreversibly through covalent linkage. Proteolytic digests of dehydro‐N‐acetyldopamine‐treated cuticle released peptide‐bound catechols. Such cuticle which on acid hydrolysis yielded ketocatechols consistent with the binding of dehydro‐N‐acetyldopamine to the cuticle through its side chain. Based on these results, the mechanisms of oxidation of 1,2‐dehydro‐N‐acetyldopamine by nonenzymatic and enzymatic systems are discussed.