The Calvin cycle has three main stages:
Carboxylation This is catalysed by rubisco, the most abundant protein (and subsequently enzyme) on Earth (and the known universe). This catalyses the conversion of ribulose-1,5-bisphosphate to 3-phosphoglycerate. Very high concentrations of rubisco are required for this reaction, due to its very slow rate.
Reduction Reduction converts 3-phosphoglycerate to glyceraldehyde-3-phosphate, through 1,3-bisphosphoglycerate. 3-phosphoglycerate kinase catalyses the conversion of 3-phosphoglycerate to 1,3-bisphosphoglycerate. Glyceraldehyde-3-phosphate dehydrogenase catalyses the conversion of 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate. This process requires ATP, from the light reaction of photosynthesis. NADPH is also used.
Regeneration Five of the six glyceraldehyde-3-phosphate molecules are used to regenerate ribulose-1,5-bisphosphate. The remaining glyceraldehyde-3-phosphate molecule is transferred to further metabolic reactions.