Kinetics and Regulation of Sarcoplasmic Reticulum ATPase

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Abstract
The measurement of ATP binding to the sarcoplasmic reticulum membrane [rabbit] reveals that the Ca pump possesses 1 high affinity (Kd = 2-3 .mu.M) site. Competition with substrate analogs show the high specificity of that site. At high ATP concentration another class of site can be detected with a much higher Kd (Kd .apprxeq. 500 .mu.M). This class of sites is of low specificty and ATP is easily displaced by other polyphosphates. The steady state rate of ATP cleavage is measured in the presence of ATP analogs. The catalysis is due to the high affinity site. The activation of the hydrolysis rate at high substrate concentration may be related to the effect of binding of ATP to the weak sites. The effect of ATP analogs for various ATP concentration supports this hypothesis.