Evidence of a dissociative S N1(P) mechanism of phosphoryl transfer by rabbit muscle pyruvate kinase

Publisher Website
Google Scholar
Abstract
Adenosine 5′-[αβ-18O,β-18O2]triphosphate has been prepared and used to investigate the mechanism of action of rabbit muscle pyruvate kinase. In the presence of pyruvate kinase and pyruvate, randomisation of the β-18O2 labels with the βγ-O bridge occurs as expected. However randomisation also occurs in the presence of the potent inhibitor oxalate, an analogue of enol pyruvate, and also in the absence of pyruvate or a pyruvate analogue. Since there is evidence against the involvement of a phosphoenzyme intermediate in the reaction pathway of pyruvate kinase, the results indicate that phosphoryl transfer in pyruvate kinase occurs by a dissociative SN1(P) mechanism, involving the transient high energy but tightly enzyme bound metaphosphate ion intermediate. The rate constants for the pyruvate kinase catalysed 18O-redistribution in adenosine 5′-[αβ-18O,β-18O2]triphosphate alone and in the presence of oxalate and pyruvate are 1.1 × 102 min–1, 2.0 × 102 min–1, and 2.0 × 103 min–1 respectively.

This publication has 18 references indexed in Scilit: