The water proton relaxation rates observed for the binary gadolinium-pyruvate kinase complex were examined as a function of temperature and frequency. The correlation times for the binary complex Tc* over a variety of temperatures and frequencies ranged from 0.18 to 0.68 nsec as estimated from the Solomon-Bloembergen equations. These values are very similar to the values reported for the electron spin relaxation time (Ts) for gadolinium. Thus it is concluded that the Tc* for the binary enzyme complex is determined primarily by the Ts of gadolinium. The vinyl protons of P-enolpyruvate are broadened in the presence of the gadolinium-pyruvate kinase complex indicating P-enolpyruvate binding, yet no change in the water proton relaxation enhancement is detected. On the basis of T2-1 values of the vinyl protons of P-enolpyruvate measured by high-resolution proton magnetic resonance and calculation of the proton-paramagnetic ion distance, it is concluded that a ternary P-enolpyruvate complex does form, but the structure of the ternary complex cannot be uniquely determined at present.
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