A coupled reaction catalyzed by the enzymes transketolase and transaldolase.

The formation of pentose phosphate from hexose monophosphate involves either the oxidative pathway from glucose 6phosphate through 6-phosphogluconate or the series of nonoxidative transfer reactions catalyzed by transketolase and transaldolase, in which sedoheptulose 7-phosphate is an intermediate (1). In mammalian tissues the nonoxidative pathway appears to play a major role (2-5), accounting for the synthesis of more than 50% of the ribose of ribonucleic acid and the acidsoluble nucleotides. Pentose phosphate synthesis from hexose monophosphate by the nonoxidative pathway has been presumed to involve the following sequence of reactions (1) :