RESUMO
The substrate specificity, physico-chemical, and kinetic properties of the trans-sialidase from Trypanosoma cruzi have been investigated. The enzyme demonstrates activity towards a wide range of saccharide, glycolipid, and glycoprotein acceptors which terminate with a beta-linked galactose residue, and synthesizes exclusively an alpha 2-3 sialosidic linkage. Oligosaccharides which terminate in Gal beta 1-4(Fuc alpha 1-3)GlcNAc, Gal beta 1-3(Fuc alpha 1-4)GlcNAc, or Gal alpha 1- are not acceptor-substrates. The enzyme utilizes alpha 2,3-linked sialic acid when the donor species is an oligosaccharide and can also transfer, at a low rate, sialic acid from synthetic alpha-sialosides such as p-nitrophenyl-alpha-N-acetylneuraminic acid, but NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)Glc is not a donor-substrate. The trans-sialidase has an apparent pH optimum of 7.9 and a temperature optimum of 13 degrees C. The kinetic properties of the enzyme suggest that the trans-sialylation reaction may occur via a rapid equilibrium random or steady-state ordered mechanism. A method for immobilizing the enzyme is described together with examples of its use for the synthesis of oligosaccharide and glycoprotein precursors of sialyl-Lewis and sialyl-Lewis.
Assuntos
Glicoproteínas , Neuraminidase/metabolismo , Trypanosoma cruzi/enzimologia , Sequência de Aminoácidos , Animais , Configuração de Carboidratos , Sequência de Carboidratos , Cromatografia de Afinidade , Eletroforese em Gel de Poliacrilamida , Indicadores e Reagentes , Cinética , Dados de Sequência Molecular , Peso Molecular , Neuraminidase/isolamento & purificação , Oligopeptídeos/síntese química , Oligossacarídeos/metabolismo , Especificidade por Substrato , TermodinâmicaRESUMO
Cantharidin, a potent defensive chemical, is present in all ten life stages of the blister beetle Epicauta funebris. The first five larval stages accumulate cantharidin as they feed and grow in size. When disturbed, they exude cantharidin in a milky oral fluid, not in hemolymph which adult beetles reflexively discharge from leg joints. Two subsequent larval stages and the pupa do not feed, grow, regurgitate, or change in their defensive reserves (110 micrograms cantharidin/insect, regardless of sex). Adult beetles kept in isolation for 60-90 d exhibit a pronounced sexual dimorphism in cantharidin production: the male biosynthesizes about 17 mg of the toxin, representing 10% of his live weight, whereas the female actually loses most of her defensive reserves. But in the wild a female beetle repeatedly acquires cantharidin as copulatory gifts from her mates.
Assuntos
Cantaridina/metabolismo , Besouros/fisiologia , Fatores Etários , Animais , Cromatografia Gasosa , Feminino , Larva , MasculinoRESUMO
Biosynthesis of cantharidin in a blister beetle, Lytta polita, is effectively inhibited by 6-fluoromevalonate. Inhibition is attributed specifically to the fluorine substituent. Biochemical inhibition has not been demonstrated previously for an arthropod's defensive substance.
Assuntos
Cantaridina/metabolismo , Besouros/metabolismo , Ácido Mevalônico/análogos & derivados , Animais , Besouros/efeitos dos fármacos , Masculino , Ácido Mevalônico/metabolismo , Ácido Mevalônico/farmacologia , ReproduçãoRESUMO
Cantharidin, a potent vesicant and antifeedant, is identified for the first time in two oedemerid beetles from the western hemisphere. Amounts of the substance per beetle were found to range from 2 to 7 µg inHeliocis repanda and from 15 to 35 µg inOxycopis thoracica. Females had two to three times more cantharidin than males of the same species. Cantharidin loads of these beetles are sufficient to irritate human skin.
