The phosphorylation potentials generated by respiring Ehrlich ascites tumor mitochondria

Abstract

The extra- and intramitochondrial phosphorylation potentials (Δ G p(out) and Δ G p(in), respectively) generated by respiring Ehrlich ascites tumor mitochondria were determined, using succinate, pyruvate + malate, ascorbate + N,N,N′,N′-tetramethyl- p-phenylenediamine, and ascorbate + ferrocyanide as substrate systems. Values of Δ G p(out) exceeding 15 kcal mol −1 (62.8 kJ mol −1) in post-ADP state 4 respiration were found with succinate as substrate, in agreement with data on normal rat liver mitochondria. ΔG p(out) values exceeding 15 kcal mol −1 (62.8 kJ mol −1) were also observed with ascorbate + TMPD or ascorbate + ferrocyanide as substrates. Slightly lower values of Δ G p(out) were found with the NAD-linked substrates pyruvate + malate. The intramitochondrial Δ G p(in) developed by respiring Ehrlich ascites tumor mitochondria respiring on succinate approached 12 kcal mol −1 (50.2 kJ mol −1), in agreement with reported values on rat liver mitochondria. The prior accumulation of Ca 2+ and phosphate by the Ehrlich cell mitochondria did not lower the extramitochondrial Δ G p(out) developed after a subsequent addition of ADP. Although the rate of oxidative phosphorylation of Ehrlich ascites tumor cells is reduced by intramitochondrial Ca 2+ and phosphate ( Villalobo and Lehninger (1980) J. Biol. Chem., 255, 2457–2464 ) they are still capable of generating ATP in the suspending medium against a high thermodynamic gradient, as expressed by the [ATP]/[ADP][ P i]mass action ratio.