Acylphosphatase induced modifications in the functional properties of erythrocyte membrane sodium pump.
Biochim Biophys Acta
; 1147(1): 19-26, 1993 Apr 08.
Article
em En
| MEDLINE
| ID: mdl-8385494
ABSTRACT
Human red cell acylphosphatase actively hydrolyzes the Na+/K(+)-ATPase phosphoenzyme from erythrocyte membrane. This effect occurred with amounts of acylphosphatase (up to 10 units/mg membrane protein) within the physiological range, and the low value of the apparent Km (0.147 +/- 0.050 microM) indicates that the enzyme has a high affinity for this substrate. When added at the above concentration to inside out vesicles from human erythrocytes, acylphosphatase significantly enhanced the rate of strophantidine-sensitive ATP hydrolysis. The same amounts of acylphosphatase stimulated, although to a lower extent, the rate of ATP-dependent 22Na+ influx (normal efflux). Thus, the calculated stoichiometry for Na+/ATP was 2.68 in the absence of acylphosphatase and 1.06 in the presence of 10 units/mg vesicle protein of the enzyme. Conversely, acylphosphatase addition strongly decreased the rate of ATP-dependent 86Rb+(K+) efflux (normal influx) which, with 10 units/mg vesicle protein, was almost suppressed. As a consequence, the Na+/Rb+ ratio, calculated as 1.52 in the absence of acylphosphatase rose to 72.5 in the presence of 10 units/mg vesicle protein of this enzyme. These results suggest that, because of its hydrolytic activity on the phosphoenzyme intermediate, acylphosphatase 'uncouples' erythrocyte membrane Na+,K+ pump. Possible mechanisms for this effect are discussed.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Hidrolases Anidrido Ácido
/
ATPase Trocadora de Sódio-Potássio
/
Monoéster Fosfórico Hidrolases
/
Membrana Eritrocítica
Limite:
Humans
Idioma:
En
Ano de publicação:
1993
Tipo de documento:
Article