IP Integument

Evidence for a catechol-?-alanyl ligase in insects

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

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

The presence of sclerotization precursors in the cuticle, namely N-?-alanyldopamine (NBAD), N-acetyldopamine (NADA) and N-?-alanylnorepinephrine (NBANE) has been described in a number of insects. We recently studied the biosynthesis of N-?-alanyldopanine (NBAD) by insect integument. This is the main catecholamine conjugate involved in the brown tanning of Ceratitis capitata puparium. We have analyzed the properties of the enzyme responsible of NBAD synthesis, NBAD synthase and found that it is difficult to characterize due to unstability at temperatures higher than –65 0 C. We demonstrate here that the same insect epidermis preparations containing the NBAD synthase was able to synthesize NBANE when incubated with Norepinephrine (NE) and ?-alanine. From different kind of evidences like kinetics data, heat-denaturation assays and absence of both activities in the melanic mutants Ceratitis capitata niger and Drosophila melanogaster ebony, it seems that the same protein might be responsible for the synthesis of both substances NBAD and NBANE. Thus pointing to the possibility of an enzyme of broad specificity, that we should call catecholamine-?-alanine-ligase (CBAL), being capable of processing alternative substrates. Other enzymes of the catecholamine pathway like the aromatic aminoacid decarboxylase and the catechol N-acetyltransferase show similar unspecificity. The only reported enzyme having catalytic characteristics related to CBAL is the mammalian carnosine synthase, that conjugates ?-alanine with histidine. We tested our insect extracts aiming at synthesizing carnosine (?-alanine- histidine) and so far negative results were obtained in several conditions. Moreover, preliminary results show that the CBAL activity might be present in neural tissue where the unknown physiological role of the synthesized products must be completely different from the one in cuticle sclerotization .

Index terms: Ceratitis capitata, metamorphosis,catecholamines, sclerotization

Copyright: The copyrights of this original work belong to the authors (see right-most box in title table). This abstract appeared in Session 13 – INSECT PHISIOLOGY, NEUROSCIENCES, IMMUNITY AND CELL BIOLOGY Symposium and Poster Session, ABSTRACT BOOK II – XXI-International Congress of Entomology, Brazil, August 20-26, 2000.