Phosphoketopentose epimerase

Fig, 17.6 Hexose monophosphate pathway. 1, glucose-6-P-dehydrogenase 2, 6-P-gluconolactonase 3,6-P-gluconate dehydrogenase 4, phosphoribose isomerase 5, phosphoketopentose epimerase 6, transketolase 7, transaldolase TPP, thiamine pyrophosphate. 

Epimerase. Another rearrangement of the pentose phosphate molecule was recently discovered. This involves an isomerization at carbon 3, to form xylulose-5-phosphate (IV). The enzyme responsible has been named phosphoketopentose epimerase. The equilibrium of the epimerase favors slightly the formation of xylulose. The isomerization of the aldose and ketose forms may be presumed to proceed via an ene-diol, as was considered for the isomerization of hexoses. Such a mechanism may also be involved in the synthesis and utilization of arabinose. A comparable mechanism may be invoked for the inversion at carbon 3. Evidence for... 

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