The effective proton conductance of the inner membrane of mitochondria from brown adipose tissue. Dependency on proton electrochemical potential gradient

Abstract

The nucleotide-sensitive H+ (OH-) conducting pathway of mitochondria from the brown-adipose tissue of cold-adapted guinea-pigs passes an effective proton current which is directly proportional to the proton electrochemical gradient. At 23 degrees C and pH 7.0 this conductance is 16 nmol H+ - min-1 - mg-1 - mV-1. Addition of 0.2 mM GDP results in a conductance which is linear and low (0.7 nmol H+ - min-1 - mg-1 - mV-1) until deltamicronH+ exceeds 220 mV. At higher values of deltamicronH+, which can be attained by glycerol 3-phosphate oxidation but not palmitoyl-L-carnitine plus malate oxidation, the membrane conductance greatly increases, effectively limiting the maximal deltamicronH+ to 240 mV. High glycerol 3-phosphate concentrations which have the thermodynamic potential to exceed this value of deltamicronH+ instead create a greatly increased rate of controlled respiration. The generality and significance of this device to limit deltamicronH+, and its relation to the nucleotide-sensitive conductance, are discussed.