The regulatory properties of kidney pyruvate dehydrogenase complex components

The activities of the enzyme components of the pyruvate dehydrogenase complex are affected to different extents by changes in ionic strength and pH. At pH 7.4 the optimum activity of pyruvate dehydrogenase (E1), dihydrolipoamide acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3) occur in the ranges of ionic strengths of 0.06-0.08, 0.01-0.02, and 0.10-0.15 M, respectively. The activity of dihydrolipoamide dehydrogenase is least sensitive to changes in the ionic strength of the assay medium. At constant ionic strength (0.15 M) the optimum activity of E1, E2, and E3 occur at pH 7.4, 7.0, and 8.0, respectively. Changes in pH mostly affect the dihydrolipoamide acetyltransferase activity. Cl- and HCO3- anions inhibit the activity of pyruvate dehydrogenase. In the presence of 80 mM Cl- or HCO3- ions the activity of E1 is inhibited by 25 and 10% respectively. K+, Na+, and HPO4(2-) ions affect the activity of dihydrolipoamide acetyltransferase. The activity of this enzyme component is stimulated by 28 and 25% in the presence of 80 mM K+ and Na+ cations, respectively. HPO4(2-) stimulates the dihydrolipoamide acetyltransferase in a calcium-dependent manner. In the presence of 20 mM HPO4(2-) the activity of the dihydrolipoamide acetyltransferase increases 20 and 40% in the absence and presence of 0.1 mM Ca2+, respectively. The activity of dihydrolipoamide dehydrogenase is not affected by K+, Na+, HPO4(2-), Cl-, or HCO3-.