Activity of the mammalian pyruvate dehydrogenase complex is regulated by phosphorylation-
dephosphorylation of three specific serine residues (site 1, Ser-264; site 2, Ser-271; site 3,
Ser-203) of the α subunit of the pyruvate dehydrogenase (E1) component. Phosphorylation
is carried out by four pyruvate dehydrogenase kinase (PDK) isoenzymes. Specificity of the
four mammalian PDKs toward the three phosphorylation sites of E1 was investigated using
the recombinant E1 mutant proteins with only one functional phosphorylation site present …