Alternative definition : KEGG: The pentose phosphate pathway is a process of glucose turnover that produces
NADPH as reducing equivalents and pentoses as essential parts of nucleotides. There
are two different phases in the pathway. One is irreversible oxidative phase in which
glucose-6P is converted to ribulose-5P by oxidative decarboxylation, and NADPH is
generated. The other is reversible non-oxidative phase in which phosphorylated sugars
are interconverted to generate xylulose-5P, ribulose-5P, and ribose-5P. Phosphoribosyl
pyrophosphate (PRPP) formed from ribose-5P is an activated compound used in the biosynthesis
of histidine and purine/pyrimidine nucleotides. This pathway map also shows the Entner-Doudoroff
pathway where 6-P-gluconate is dehydrated and then cleaved into pyruvate and glyceraldehyde-3P.;