The second phase of the Calvin cycle is Reduction. The PGA obtained from the carboxylation phase is used in the reduction phase. The reactions of reduction phase lead to the formation of glucose. 3-phosphoglycerate (PGA, a carboxylic acid) is first phosphorylated into 1,3-bisphosphoglycerate by enzyme 3-phosphoglycerate kinase. This is followed by a reduction of 1,3-bisphosphoglycerate catalyzed by glyceraldehyde 3-phosphate dehydrogenase enzyme into glyceraldehyde 3-phosphate (aldehyde). NADPH serves as electron donor here.