Reexamination of the mechanisms of oxidative transformation of the insect cuticular sclerotizing precursor, 1,2-dehydro-N-acetyldopamine |
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| Authors: | Adal Abebe Dong Zheng Jason Evans Manickam Sugumaran |
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| Institution: | 1. Department of Biology, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125, USA;2. Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Blvd., Boston, MA 02125, USA;1. Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore;2. School of Bioscience and Biotechnology, Tokyo University of Technology, Katakura 1404-1, Hachioji, Tokyo 192-0982, Japan;1. Beijing Key Laboratory of Lignocellulosic Chemistry, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, PR China;2. School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China;3. State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210, USA;1. School of Life Sciences, Xiamen University, Xiamen, Fujian 361102, China;2. State Key Laboratory of Stress Cell Biology, Xiamen University, Xiamen, Fujian 361102, China;3. Medical College, Xiamen University, Xiamen, Fujian 361102, China;1. Department of Biology, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125-3393, United States;2. Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125-3393, United States;3. School for the Environment, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125-3393, United States;1. College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018, China;2. Center of Materials Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China |
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| Abstract: | 1,2-dehydro-N-acetyldopamine (dehydro NADA) is an important catecholamine derivative formed during the sclerotization of insect cuticle. Earlier we have reported that tyrosinase-catalyzed oxidation of dehydro NADA produces a reactive quinone methide imine amide that forms adducts and cross-links through its side chain, thereby accounting for sclerotization reactions. Recently, laccase has also been identified as a key enzyme associated with sclerotization. Hence, we re-examined oxidation of dehydro NADA by tyrosinase and laccase using high performance liquid chromatography – tandem mass spectrometry. Tyrosinase-catalyzed oxidation of dehydro NADA not only generated dimers as reported earlier, but also generated significant amounts of oligomers. The course of laccase-catalyzed oxidation of dehydro NADA significantly differed from the tyrosinase reaction kinetically and mechanistically. Laccase failed to produce any detectable quinone or quinone methide as the primary two-electron oxidation product. Since laccases are known to generate primarily semiquinones as the initial products, lack of accumulation of two-electron oxidation products indicated that laccase reaction is primarily occurring via free radical coupling mechanism. Consistent with this proposal, laccase-catalyzed oxidation of dehydro NADA, resulted in the production of largely dimeric products and failed to produce any significant amount of oligomeric materials. These studies call for radical coupling as yet another major mechanism for sclerotization of insect cuticle. |
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