Integument

ß-Alanyl derivatives in cuticle and neural tissue

L. A. Quesada-Allué, P. Wappner and M. M. Pérez

Instituto de Investigaciones Bioquímicas, (Fundación Campomar, CONICET and University of Buenos Aires), Patricias Argentinas 435, Bs Aires (1405), Argentina

In brown insect cuticles of several insects, N-ß-alanylcatecholamines seem more important precursors for sclerotization than N-acetylcatecholamines. N-?-alanyldopamine (NBAD) and N-?-alanylnorepinephrine (NBANE) are the main ?-alanyl derivatives found in most dictyopteran, dipteran and lepidopteran, NBAD being the more abundant in several cuticles. NBAD is also a precursor of papilochrome II, a pteridine formed in lepidopteran wings by conjugation with kynurenine. 1,2-dehydro-NBAD has been reported as intermediate in Calliphora cuticular sclerotization. Other ?-alanyl derivatives unrelated to cuticle have been described in insects, like sarcophagine (?-ala-Tyr) in Sarcophaga and the novel antibacterial substance N-ß-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD) in the same flesh fly. Glycosyl-conjugates of NBAD and NBANE have been found in haemolymph, whereas these N-ß-alanylcatecholamines also occur in neural tissue. Recent results on the synthesis of these and other conjugates by a putative catecholamine-?-alanine ligase (CBAL), able to use alternative substrates, will be discussed. This enzyme is extremely unstable and seems responsible of the synthesis of both NBAD and NBANE in Ceratitis capitata tissues. Similar enzymatic activities have been measured in Drosophila melanogaster and other insects. Melanic mutants like Drosophila ebony and Ceratitis niger will be revisited and their expression discussed.

Index terms: N-ß-alanylcatecholamines; sclerotization; dopamine; norepinephrine

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