Arthropoda (Insecta, Crustacea and Arachnida) are the most abundant form of animal life on the planet, with perhaps a million species. The digestive system of this group of animals is one of the most important contact surfaces with environment and many of the adaptations, which allowed the occupation of diverse niches, occurred in the digestive system. Characterization of Arthropoda digestion showed that different Arthropoda groups present particularities in both, morphological and molecular aspects of digestion. The knowledge about Arthropoda digestion is large to Insect and Crustacea (Terra and Ferreira, 2005). However, there is a lack of data about Arachnida digestion, mainly the molecular aspects of digestion, making impossible comparative and evolutive studies between Arachnida and the other Arthropoda digestion. Scorpione is one of the oldest terrestrial orders, which makes this group a very interesting model to comparative studies. A large part of digestion in Arachnida occurs extra-orally. Extra-oral digestion is classified in two distinct groups: type I, the chemical liquefaction of prey performed entirely within the preys body, which in effect turns the prey exoesqueleton into an extension of the predators gut or type II, the mechanical disassembly of prey and chemical digestion of the nutrient-rich components within a region outside the predators mouth but within the sphere of its mouthparts (Cohen, 1995). Tityus serrulatus (yellow scorpion; Buthidae) will be used on this project as a model of Arachnida digestion. This scorpion is widely distributed in Brazil and causes 8.000 accidents of human envenomation. Besides that, with the exception of amylase from Heterometrus scaber (Vijayalekshmi and Kurup) and recent purification of Scorpio maurus lipase (Zouari et al., 2005), there is no knowledge about which enzymes are involved in scorpion digestion and properties of these enzymes. Peptidases (peptide-hydrolases, E.C. 3,4) are the enzymes that catalyze the hydrolysis of peptide bond and are divided on 5 mechanistic classes: serine, cysteine, aspartic, threonin and metalo peptidase (Barrett, et al., 2003). Peptidases may also be divided in two groups: the exopeptidases including aminopeptidases, carboxypeptidases and dipeptidases; and the endopeptidases that cleave internal peptide bonds of proteins and present different specificities. In this project peptidases from Tityus serrulatus hepatopancreas will be detected, classified and separated by electrophoresis and chromatographies and tested against natural and synthetic substrates and inhibitors in order to identify which are the main peptidases involved in digestion in this Arachnida.
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