Dark reactions steps chlorophylls

The first step in the assimilation of COj is assumed by Ruben, Kamen and coworkers to involve a non-photochemical reaction, catalyzed enzymically and resulting in the addition of CO2 to a large molecule. The process is initiated rapidly in the dark and gradually decreases in rate. These results suggest that it is reversible. Since no correlation could be found between the concentration of chlorophyll in the leaves and the COj uptake, it is believed that chlorophyll is not concerned with this initial reaction. Chlorophyll is believed to catalyze a second reaction involving the reduction of the carboxylic compound to an alcohol or polyalcohol. This second reaction, believed to occur in the presence of light, is endothermic and irreversible. 

---