Estudo do efeito da serie homologa de surfatantes anionicos e cationicos e de compostos purinicos na atividade da proteina tirosina fosfatase de baixa massa molecular relativa do rim bovino

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

Protein tyrosine phosphatase (PTP) plays a key event in the regulation of cell division, differentiation, and development. Among the members of this superfamily, the low Mr protein tyrosine phosphatases (LMr PTPs) have been found in mammals, yeast and various bacteria. This work describes the effect of the homologous series of n-alkyl sulfates (C8-C14, anionic surfactants) and n-alkyl trimethylammonium bromides (C12-C16, DTAB, TTAB, and CTAB, cationic surfactants) on the enzyme activity , thermal stability and denaturation. In contrast to cationic surfactants, the effect of anionic surfactants was below the cmc and independent of pH and ionic strength. The inactivation by SDS (irreversible) and TTAB (reversible) was prevented by inorganic phosphate. The protein melting point increased in the presence of cationic, but decreased in the presence of anionic surfactants. The effect of purinic compounds on the enzyme activity depended on their chemical structures; guanosine, adenine, and inosine were activators while guanine and uric acid were inhibitors. The enzyme activation by guanosine, of the mixed type, promoted a decreasing in the activation energy and the enzyme thermal stability .Guanosine bind to the enzyme in two different sites with a calorimetric enthalpy of -80 kJ mol-1. The enzyme activation was independent of pH, but dependent on the substrate structures. The uric acid reversible inhibition was dose, time and substrate structure dependent (the uric acid concentration that inhibited half of the enzyme activity was, respectively, 0.2 and 1.0 mM for tyrosine phosphate and pNPP). The inhibition was of the mixed type (Kic and Kiu of 0.37 and 1.1 mM, respectively), and produced a shift in the optimum pH (from 5.0 to 6.5). Uric acid inhibition occurred near or at the active site since inorganic phosphate caused a fully protective effect. Soy and castor beans seeds acid phosphatases, shark and bovine milk acid phosphatases (with carbohydrate content) were insensitive to uric acid, even after 10 minutes of preincubation.

ASSUNTO(S)

enzimas inibição cinetica quimica

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