<Li> Fixation of a third CO generates two more G3P . The ketose S7P has two carbons removed by transketolase, giving ribose - 5 - phosphate (R5P), and the two carbons remaining on transketolase are transferred to one of the G3P, giving another Xu5P . This leaves one G3P as the product of fixation of 3 CO, with generation of three pentoses that can be converted to Ru5P . </Li> <Li> R5P is converted into ribulose - 5 - phosphate (Ru5P, RuP) by phosphopentose isomerase . Xu5P is converted into RuP by phosphopentose epimerase . </Li> <Li> Finally, phosphoribulokinase (another plant - unique enzyme of the pathway) phosphorylates RuP into RuBP, ribulose - 1, 5 - bisphosphate, completing the Calvin cycle . This requires the input of one ATP . </Li> <P> Thus, of six G3P produced, five are used to make three RuBP (5C) molecules (totaling 15 carbons), with only one G3P available for subsequent conversion to hexose . This requires nine ATP molecules and six NADPH molecules per three CO molecules . The equation of the overall Calvin cycle is shown diagrammatically below . </P>

Two products of the light reaction that enter the calvin cycle