Dynamic reversal of enzyme carboxyl group phosphorylation as the basis of the oxygen exchange catalyzed by sarcoplasmic reticulum adenosine triphosphatase

Abstract

Ms mixing and quenching experiments demonstrated an apparent t1/2 [half-time] for the labeling of phosphorylated sarcoplasmic reticulum [rabbit skeletal muscle] ATPase by 32Pi at pH 6 and 30.degree. C of 30-40 ms. Under the same conditions, the rate of exchange of water O2 with inorganic phosphate (Pi) was about 40 mol of H2O exchanged with Pi/106 g of protein per s. Theoretical equations were developed for the expected 32P-labeling pattern given various comparative rates of flux between Pi and the Michaelis complex and between the Michaelis complex and phosphorylated enzyme. The rapid reversal of the formation of the phosphorylated enzyme was a major source of the O2 exchange and were consistent with such reversal being the only source.