ACYLPHOSPHATASE INDUCED MODIFICATIONS IN THE FUNCTIONAL-PROPERTIES OF ERYTHROCYTE-MEMBRANE SODIUM-PUMP

被引:22
|
作者
NASSI, P
MARCHETTI, E
NEDIANI, C
LIGURI, G
RAMPONI, G
机构
[1] Dipartimento di Scienze Biochimiche, Università di Firenze, Florence
关键词
RED CELL MEMBRANE; SODIUM PUMP; ATPASE; TRANSPORT ACTIVITY; ACYLPHOSPHATASE;
D O I
10.1016/0005-2736(93)90311-M
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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 K(m) (0.147 +/- 0.050 muM) 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 Na-22+ 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 Rb-86+(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.
引用
收藏
页码:19 / 26
页数:8
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