JBC, Vol. 254, Issue 11, 4352-4358, Jun, 1979
The proton stoichiometry of electron transport in Ehrlich ascites tumor mitochondria
A. Villalobo and A. L. Lehninger
Initial rate measurements of the stoichiometric relationships between H+
ejection, K+ and Ca2+ uptake, and electron transport were carried out on
mitochondria from Ehrlich ascites tumor cells grown in mice. With succinate
as substrate and N-ethylmaleimide to prevent interfering H+ reuptake via
the phosphate carrier, close to 8 H+ were ejected per oxygen atom reduced
(H+/O ejection ratio = 8.0); with the NAD-linked substrates pyruvate or
pyruvate + malate, the H+/O ejection ratio was close to 12. The average
H+/site ratio (H+ ejected/2e-/energy-conserving site) was thus close to 4.
The simultaneous uptake of charge-compensating cations, either K+ (in the
presence of valinomycin) or Ca2+, was also measured, yielding average
K+/site uptake ratios of very close to 4 and Ca2+/site ratios close to 2.
It was also demonstrated that each calcium ion enters the respiring tumor
mitochondria carrying two positive electric charges. These stoichiometric
data observed in mitochondria from Ehrlich ascites tumor cells thus are in
complete agreement with similar data on normal rat liver and rat heart
mitochondria and suggest that the H+/site ratio of mitochondrial electron
transport may be 4 generally. It was also observed that the rate of deltaH+
back-decay in anaerobic tumor mitochondria following oxygen pulses is some
6- to 8-fold greater than in rat liver mitochondria tested at equal amounts
of mitochondrial protein.
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