THE EFFECT OF PHOSPHORYLATION ON PYRUVATE-DEHYDROGENASE

Phosphorylation of the pyruvate dehydrogenase component (E1) of the mu scle pyruvate dehydrogenase complex (PDC) by E1-kinase inhibits substr ate conversion both in oxidative and non-oxidative reactions. Circular dichroism spectra were used to monitor the effect of phosphorylation on the following stages of the process: holoform formation from apo-E1 and thiamine pyrophosphate (TPP), substrate binding and active site d eacetylation, It has been shown that phosphorylation of E1 reduces its affinity for TPP and prevents holo-E1 interaction, with pyruvate. Pho sphorylated and dephosphorylated PDC convert 2-hydroxyethyl-TPP in sim ilar ways involving half of their active sites; all active sites of El function in the presence of deacetylating agents. The data obtained s uggest that the phosphorylation and substrate binding sites interact w ith each other.