Comparative study of the aminopeptidases purified from liver of patients with normal and altered serum aminotransferases levels. / Estudo comparativo entre as aminopeptidases purificadas de fígado de pacientes com as aminotransferases séricas normais e alteradas.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Enzymes like aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are released by the liver during several pathologies and have been used in laboratory tests to evaluate hepatic damage. Aminopeptidases, enzymes that hydrolyze peptide bonds in N-terminal amino acids of proteins, are important in protein metabolism and might have altered activity during hepatic injury. The aim of this work was to verify if there is a relationship between serum transaminases levels and the aminopeptidases present in human liver. In normal human liver it was identify a basic aminopeptidase (65 kDa) and a neutral aminopeptidase (43 kDa) similar to the aminopeptidases found in liver of patients with altered aminotransferase levels. These enzymes are monomeric metalo-aminopeptidases, with optimum pH 7,0 and are partially inhibited by the cyclic compounds sodium desoxicolate and hydrocortisone succinate. The neutral aminopeptidases were competitively inhibited by the antibiotics amastatin (Ki = 0,1 x 10-8 M), actinonin (Ki = 0,9 x 10-7 M) and bestatin (Ki = 0,7 x 10-6 M) while the basic aminopeptidases were competitively inhibited by bestatin (Ki = 0,1 x 10-5 M) and puromycin (Ki = 0,6 x 10-5 M). However, it was also identified a leucine aminopeptidase, not found when AST and ALT are at basal levels, that is activated by the anti-inflammatory drug indomethacin and by the others cyclic compounds tested. Actinonin, amastatin, bestatina and puromycin did not inhibit this enzyme, which has optimum pH 8.0 and has disulfides bonds and SH groups important for its activity. This leucine aminopeptidase is a dimer with molecular mass of 100 kDa consisted of 60 kDa monomers. Previous studies (Serwold et al., 2002), identified in mouse liver a leucine-specific aminopeptidase not inhibited by puromycin that is activated by INF-γ and is involved in antigen processing, modulating the citotoxic T cells response, indicating that the leucine aminopeptidase found in the liver of patients with altered aminotransferase levels might be related to the immune response during hepatic injury. Therefore, the hepatic injury revealed by the increased serum aminotransferases showed a leucine aminopeptidase not present in the normal liver.

ASSUNTO(S)

1. aminopeptidases. 2.aminotransferases. 3. fígado. 4. dano hepático. 5. leucina aminopeptidase / isolamento e purificação. biologia molecular

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