Catalysis of pentose phosphate pathway reactions by cytoplasmic fractions from muscle, uterus and liver of the rat, and the presence of a reduced nicotinamide–adenine dinucleotide phosphate–triose phosphate oxidoreductase in rat muscle

Abstract

1. The enzymes of the pentose phosphate pathway were assayed in supernatant fractions from rat muscle, liver and uterus. 2. On incubation of ribose 5-phosphate with uterus and liver supernatants, triose phosphate, sedoheptulose 7-phosphate and hexose monophosphate accumulated. 3. When a muscle supernatant was used, glycerol 3-phosphate instead of triose phosphate appeared and there was a negligible accumulation of hexose monophosphate. 4. Hexose monophosphate production from ribose 5-phosphate was also followed by measuring NADP+ reduction in the presence of an excess of phosphoglucose isomerase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. 5. With a muscle supernatant, NADPH was reoxidized as rapidly as it was formed owing to the presence of a NADPH–triose phosphate oxidoreductase. 6. A modification of the pentose phosphate pathway in skeletal muscle incorporating this enzyme is proposed.