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The pentose phosphate pathway contains two stages, oxidative and non-oxidative, which is another option for glucose oxidation.

Isomerization and epimerization processes proceed in step 2 of the pentose phosphate cycle. In the presence of the enzyme ribulose-5-phosphate epimerase, ribulose-5-phosphate is transformed to xylulose 5-phosphate in this step.In a reversible route, this whole conversion process proceeds through a 1, 2-enediolate intermediate to convert xylulose 5-phosphate. In addition to pentose sugar and glucuronate interconversion, the enzyme ribulose-5-phosphate epimerase is also involved.

Hence, the enediolate intermediate in the ribulose-5-phosphate epimerase process transforms ribulose-5-phosphate to xylulose-5-phosphate.