Pentose Phosphate Pathway and Nicotinamide Adenine Dinucleotide Phosphate Overview

The pentose phosphate pathway (or, hexose monophosphate shunt) occurs in the cytosol. It includes an irreversible oxidative phase, followed by a series of reversible sugar–phosphate interconversions (Fig. 1).

In the oxidative phase, carbon 1 of a glucose 6-phosphate molecule is released as carbon dioxide (CO2), and one pentose sugar-phosphate plus two reduced nicotinamide adenine dinucleotide phosphates (NADPH) are produced. The rate and direction of the reversible reactions are determined by the supply of and demand for intermediates of the pathway. The pentose phosphate pathway provides a major portion of the body’s NADPH, which functions as a biochemical reductant. It also produces ribose 5-phosphate, required for nucleotide biosynthesis , and provides a mechanism for the conversion of pentose sugars to triose and hexose intermediates of glycolysis. No ATP is directly consumed or produced in the pathway.

Figure .1 Pentose phosphate pathway shown as a component of the metabolic map.  P = phosphate; DHAP = dihydroxyacetone phosphate.