The interaction of reduced nicotinamide–adenine dinucleotide phosphate with reduced nicotinamide–adenine dinucleotide–ubiquinone reductase from bovine heart mitochondria

Reduction of the chromophores of mitochondrial NADH-ubiquinone reductase by NADPH reaches only 50% of the extent of reduction by NADH, monitored at 450 nm. This effect is due to autoxidation of an enzyme component at a higher rate than its reduction by NADPH.