RESPIRATION OF MITOCHONDRIA OF RED AND WHITE SKELETAL MUSCLE.

Abstract

Mitochondria of guinea pig red and white skeletal muscle were isolated in a medium containing 0.25 m sucrose, 1 mm ethylenediamine tetraacetate, and 1% fraction V bovine albumin. Oxidative phosphorylation with pyruvate-malate as substrate was tightly coupled in both types of mitochondria when oxygen uptake was measured over a 2- to 4-min period with a platinum electrode. The P/O ratios approached the theoretical value of 3. Oxygen consumption was also determined manometrically with the substrates 10 mm pyruvate—1 mm malate, 10 mm succinate, 6 mm reduced nicotinamide adenine dinucleotide (NADH2), 20 mm dl-lactate, and 12–20 mm dl-α-glycerophosphate. White muscle mitochondria had a higher rate of oxygen consumption with α-glycerophosphate than with lactate, succinate, and NADH2. Those of red muscle were less active with α-glycerophosphate than with the other substrates. These results indicate that an α-glycerophosphate shuttle may couple the reactions generating NADH2 in the cytoplasm of white muscle with the mitochondrial respiratory chain. The properties of the red muscle mitochondria suggest that the direct oxidation of NADH2 may be more important in this tissue than the α-glycerophosphate shuttle.