An estimation of the proton conductance of the inner membrane of turnip (Brassica napus L.) mitochondria.

The permeability of the inner membrane of turnip mitochondria to H(+) and OH(-) ions has been investigated using an acid pulse technique. The rate of decay of a H(+) pulse across the inner membrane is exponential having first-order kinetics and gives t 1/2 values of approx 54 s at neutral pH and at 25° C. Valinomycin or 1799 alone have little effect on t 1/2 values, whereas in combination, values of <15 s are observed. Nigericin produces a similar effect. The effective proton conductance of the inner membrane near pH 7 at 25° C is 0.27 nmol H(+) min(-1) mg protein(-1) mV(-1). The results suggest that at neutral pH, the inner membrane of plant mitochondria is relatively impermeable to H(+) and OH(-) ions.