Succinyl Coenzyme A Synthetase of Pig Heart: Studies of the Subunit Structure and of Phosphoenzyme Formation

Abstract

Succinyl coenzyme A synthetase from pig heart (molecular weight approximately 75 000) gives rise to two species of subunits when subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The molecular weights of the constituent subunits are estimated to be about 42 500 and 34 500, suggesting that the enzyme is a dimer. The presence of saturating concentrations of guanosine 5′-triphosphate (GTP) results in the formation of one phosphohistidine residue per molecule of enzyme; the site of phosphorylation is in the smaller subunit. The standard free energy change for phosphorylation of the enzyme by GTP is approximately −400 cal/mol. The results point to both interesting similarities and differences in succinyl-CoA synthetases isolated from mammalian and bacterial sources.