RESUMO
A functionalized N-aryl azetidinone has been shown to inactivate human leukocyte elastase (HLE) and porcine pancreatic elastase (PPE) by an enzyme-mediated process. The inactivation is characterized by the following kinetic constants at pH 8.0 and 37 degrees C: kinact = 0.035 s-1, KI = 1.2 x 10(-4) M for HLE, 0.08 s-1 and 2.7 x 10(-4) M for PPE, respectively. Two parent molecules devoid of the latent leaving group failed to inactivate HLE and PPE and behaved as substrates of these enzymes. A suicide mechanism is postulated involving the formation of an acyl-enzyme and the simultaneous unmasking of a latent quinonimmonium methide ion which irreversibly reacts with an active site nucleophile. Moreover, the inhibitor is still effective at inhibiting elastase preabsorbed onto elastin.
Assuntos
Azetidinas/farmacologia , Neutrófilos/enzimologia , Elastase Pancreática/antagonistas & inibidores , Animais , Sítios de Ligação , Elastina/metabolismo , Cinética , Pâncreas/enzimologia , SuínosRESUMO
3-Benzyl-6-chloromethyl-3,4-dihydrocoumarin inhibits human leucocyte elastase (HLE) and porcine pancreatic elastase (PPE) through a mechanism-based process characterized by the following apparent enzyme-inhibitor dissociation constants, Ki, and limiting inactivation rate constants k2: 200 microM (HLE), 69 microM (PPE) and 5.10(-2) s-1 (HLE), 17.7.10(-2) s-1 (PPE) at pH 8.0, 37 degrees C. Bis(4-acyloxyphenyl)methane derivatives with a benzylic halogen as potential leaving group have also been synthesized and studied. They transiently inactivate PPE and HLE through the formation of an acyl-enzyme.
Assuntos
Cumarínicos/síntese química , Elastase Pancreática/antagonistas & inibidores , Inibidores de Proteases/síntese química , Animais , Cumarínicos/farmacologia , Humanos , Indicadores e Reagentes , Cinética , Leucócitos/enzimologia , Pâncreas/enzimologia , Elastase Pancreática/sangue , Relação Estrutura-Atividade , SuínosRESUMO
Adenosine uptake in the presence of some metabolic inhibitors and nucleosides has been studied. The uptake of adenosine was inhibited by oubain, phlorizin, iodoacetate and coformycin. Guanosine, on the other hand stimulated adenosine uptake to a considerable extent. Neither thymidine nor inosine caused significant change in adenosine uptake. Results of the time course assay and uptake studies at various concentrations of adenosine suggest that possibly more than one mode of uptake operates in the transport of adenosine in T. Vivax.
