Abstract
The presence of aminopeptidases and carboxypeptidases was investigated in the midgut of Spodoptera littoralis. Leucine aminopeptidase, cystenyl aminopeptidase and dipeptidyl aminopeptidase IV were found in the midgut tissue only and showed optimum activity between pH 7.5–8.5. The leucine aminopeptidase was partially purified and characterised with respect to a variety of inhibitors and substrates. It preferentially cleaved N-terminal methionine, leucine and alanine, but also cleaved other N-terminal amino acid substrates (aliphatic: Val, Gly; basic: Arg, Lys; aromatic: Phe; heterocyclic: Pro); hydrolysis of GlupNA was extremely slow. The molecular weights of leucine and cystenyl aminopeptidases were estimated to be about 116 kDa. Leucine aminopeptidase activity was inhibited by bestatin, 1,10 phenanthroline, Tris and several metal ions, notably copper (II), lead (II) and zinc (II). The ion-chelator EDTA, magnesium (II) and manganese (II) ions had relatively little effect on activity. Activity towards the carboxyesterase A substrate, HPLA, was present with an optimum activity at about pH 9.0. This activity was not inhibited by DSS. No carboxypeptidase activity could be detected using either HPA (carboxypeptidase A) or HA (carboxypeptidase B) in the presence or absence of an activator, DSS.
Published Version
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