Regulation of Pyruvate Dehydrogenase Complex Activity in Ehrlich Ascites Carcinoma Cells by Ca²⁺ and Pyruvate

G. L. Ermakov^1*, L. P. Dolgacheva², B. N. Goldstein¹, I. I. Goryanin¹, and V. P. Zinchenko²

¹Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (0967) 79-0553; E-mail: ermakov@venus.iteb.serpukhov.su

²Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (0967) 79-0509

^* To whom correspondence should be addressed.

Received March 18, 1998; Revision received November 10, 1998

---

The dependence of pyruvate dehydrogenase complex (PDC) activity on [Ca²⁺] was determined in Ehrlich ascites carcinoma cells at different pyruvate concentrations. The resulting family of curves had the following characteristics: a) bell-shaped appearance of all curves with maximum activity at 600 nM Ca²⁺; b) unchanged position of maxima with changes in pyruvate concentration; c) nonmonotonous changes in PDC activity with increasing pyruvate concentration at fixed [Ca²⁺]. Feasible mechanisms involving Ca²⁺-dependent phosphatase and kinase which are consistent with the experimental findings are discussed. To determine the steps in the chain of PDC reactions which determine the observed phenomena, a mathematical model is suggested which is based on the known data on the structural--functional relationships between the complex components--pyruvate dehydrogenase (E1), dihydrolipoyl acetyl transferase (E2), dihydrolipoyl dehydrogenase (E3), protein X, kinase, and phosphatase. To adequately describe the non-trivial dependence of PDC activity on [Ca²⁺] at different pyruvate concentrations, it was also necessary to consider the interdependence of some steps in the general chain of PDC reactions. Phenomenon (a) is shown to be due only to the involvement of protein X in the PDC reactions, phenomenon (b) to be due to changes in the activity of kinase, and phenomenon (c) to be due to dependence of acetylation and transacetylation rates on pyruvate concentration.

---

KEY WORDS: pyruvate dehydrogenase complex, calcium, mathematical model

---