RESUMEN
The effect of N1-substituted analogs of ATP on the hydrolysis of umbelliferone phosphate by Na,K-ATPase has demonstrated: analogs having a negatively charged substituent (N1-oxy- or N1-carbo-methoxy-ATP) and capable of accepting H+ induce an activation similar to that of ATP; N1-methoxy-ATP, containing an uncharged substituent, does not affect the phosphatase reaction at low concentration and inhibits it at higher concentration. It has been assumed that ATP binding to Na,K-ATPase induces formation of a hydrogen bond between the nitrogen atom at the first position of the purine base and appropriate amino acid of active centre, with a subsequent attachment of H+ to ATP, thus facilitating the transition of Na,K-ATPase from the K+- to the Na+-form.
Asunto(s)
Adenosina Trifosfato/análogos & derivados , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Adenosina Trifosfato/farmacología , Animales , Patos , Activación Enzimática , Cinética , Glándula de Sal/enzimologíaAsunto(s)
Encéfalo/enzimología , Protamina Quinasa/metabolismo , Proteínas Quinasas/metabolismo , Secuencia de Aminoácidos , Animales , Catálisis , Cromatina/metabolismo , Cromatografía de Afinidad , AMP Cíclico/análogos & derivados , AMP Cíclico/metabolismo , AMP Cíclico/farmacología , Electroforesis en Gel de Poliacrilamida , Activación Enzimática , Modelos Químicos , Peso Molecular , Protamina Quinasa/antagonistas & inhibidores , Protamina Quinasa/aislamiento & purificación , Unión Proteica , Relación Estructura-ActividadAsunto(s)
Adenosina Trifosfato/análogos & derivados , Inhibidores de Adenilato Ciclasa , AMP Cíclico/análogos & derivados , Inhibidores de Fosfodiesterasa , Inhibidores de Proteínas Quinasas , Adenosina Trifosfato/farmacología , Animales , Sitios de Unión , Fenómenos Químicos , Química , Columbidae , AMP Cíclico/farmacología , Técnicas In Vitro , Cinética , Hígado/enzimología , Modelos Biológicos , Músculos/enzimología , Conejos , RatasRESUMEN
6-Cloro-9-beta-d-ribofuranosylpurine 5'-triphosphate (CIRTP) and 6-mercapto-9-beta-d-ribofuranosylpurine 5'-triphosphate (SRTP) irreversibly inhibit adenylate cyclase from rat brain. Adenosine 5'-[beta, gamma -imido] triphosphate protects the enzyme against inactivation by CIRTP and SRTP and acts as a competitive inhibitor with respect to ATP with the Ki value 2 X 10(-4) M. Study of the pH-dependence of the rate of the enzyme inactivation by CIRTP showed that pK for the group modified by this compound is equal to 7.45. Inactivation is first order with respect to the enzyme; the saturation effect is observed at the increased concentration of CIRTP. The k2 and KI values for irreversible inhibition of brain adenylate cyclase by CIRTP were 0.25 min-1 and 1.9 X 10(-4) M, respectively. Adenylate cyclase inhibition by SRTP is also time-dependent. Partial protection against the enzyme inactivation was observed. Dithiothreitol restores the activity of SRTP-inactivated adenylate cyclase. The results obtained indicate the presence of an -SH group in the purine amino group binding area of the enzyme active site.