ATP and reduced NADP from the light-dependent reactions are used in the Calvin cycle which is a light-independent process. The three main stages are carbon dioxide fixation - the combination of carbon dioxide with 5-carbon ribulose bisphosphate (RuBP) to form a 6C compound, the splitting into two 3carbon molecules and the reduction of the glycerate phosphate subsequently formed to form triose phosphate and the regeneration of RuBP so that the cycle can continue. Rubisco, the enzyme that catalyses CO2 fixation, is the rate-limiting enzyme in photosynthesis.ATP and reduced NADP from the light dependent reactions are used to reduce glycerate phosphate (GP) to triose phosphate(TP) The triose phosphate is then used to make glucose, amino-acids and fatty acids.