Quinone methide sclerotization: A revised mechanism for β-sclerotization of insect cuticle
1987; Elsevier BV; Volume: 15; Issue: 2 Linguagem: Inglês
10.1016/0045-2068(87)90019-8
ISSN1090-2120
Autores Tópico(s)Plant Surface Properties and Treatments
ResumoMolecular mechanisms responsible for the stiffening and tanning of insect cuticle are reviewed. Two mechanisms, viz., quinone tanning and β-sclerotization, both involving catecholamine derivatives as sclerotizing precursors, are known to strengthen the cuticle. Quinone tanning mechanism invokes the generation and reactions of o-benzoquinones as the sclerotizing agents, whereas β-sclerotization dictates the activation of catecholamine side chains prior to their incorporation into cuticle. The reactive intermediate for the latter process was proposed by other workers to be 1,2-dehydro-N-acetyldopamine and its quinone. The role of these two compounds in β-sclerotization is critically evaluated. Based on our observation that incubation of cuticular enzyme from Sarcophaga bullata with 4-alkylcatechols results in the production of soluble side chain oxygenated compounds and the formation of catechol-cuticle adducts, an alternate mechanism for β-sclerotization is proposed. This mechanism calls for the generation of quinone methides, tautomers of 4-alkyl-quinones, as the initial products of oxidation of catecholamine derivatives in cuticle. Quinone methides formed spontaneously react with available nucleophiles in cuticle, resulting in the generation of catechol-cuticle adducts and side chain hydroxylated products. Further oxidation of adducts and coupling to other structural units ensure crosslinking of cuticular components. The proposed quinone methide sclerotization accounts for all the chemical observations made on the β-sclerotized cuticle.
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