Oxidative phosphorylation efficiency of mitochondria isolated from pectoralis muscle of fasted chicks. Oxygen uptake and ATP synthesis were determined at 38°C (open symbols) and at 30°C (grey symbols) with either pyruvate/malate (A) or palmitoyl-l-carnitine/malate (B). Mitochondrial fluxes were titrated by addition of increasing concentrations of ADP in the presence of glucose (20 mmol l−1) and hexokinase (1.5 U ml−1). Values are means±s.e.m. for N=5 independent mitochondrial preparations.