The non-oxidative reactions are concerned with the inter-conversion of 3−, 4−, 5−, and 7-carbon monosaccharides. Ribulose 5-phosphate is acted upon by an enzyme epimerase to produce xylulose 5-phosphate while ribose ketoisomerase converts ribulose 5-phosphate to ribose 5-phosphate. The enzyme transketolase catalyse the transfer of two carbon moiety from xylulose 5-phosphate to ribose 5-phosphate to give 3-carbon glyceraldehydes 3-phosphate and a 7-carbon sedoheptulose 7-phosphate. Transketolase depends on the coenzyme thiamine pyrophosphate (TTP) and Mg²⁺.

Transaldolase brings about the transfer of a 3-carbon fragment from sedoheptulose 7-phosphate to glyceraldehydes 3-phosphate to give fructose 6-phosphate and 4-carbon erythrose 4-phosphate. Transketolase acts on xylulose 5-phosphate and transfers 2-carbon fragment (glyceraldehydes) from it to erythrose 4-phosphate to generate fructose 6-phosphate and glyceraldehyde 3-phosphate. Fructose 6-phosphate and glyceraldehyde 3-phosphate can be further catabolised through glycolysis and TCA. Glucose may also be synthesised from these two compounds.