Figure 23.4 The regeneration of ribulose 1,5-bisphosphate. (A) A transketolase and aldolase generate the five-carbon sugars ribose 5-phosphate and xylulose 5-phosphate from six-carbon and three-carbon sugars. (B) Both ribose 5-phosphate and xylulose 5-phosphate are converted into ribulose 5-phosphate, which is then phosphorylated to complete the regeneration of ribulose 1,5-bisphosphate.