Fractionation of carbon isotopes in oxygenic photosynthesis Calvin cycle during the day, when stomata are closed to prevent water loss, and the light reactions can drive the necessary ATP and NADPH production. This pathway differs from C4 photosynthesis because CAM plants separate carbon by storing fixed CO in vesicles at night, then transporting it for use during the day. Thus, CAM plants temporally concentrate CO to improve Rubsico efficiency, whereas C4 plants spatially concentrate CO in bundle sheath cells. The distribution of plants which use CAM photosynthesis includes epiphytes (e.g., orchids, bromeliads) and xerophytes (e.g., succulents, cacti). In Crassulacean acid metabolism, isotopic fractionation combines the effects of
Photosynthesis allowing carbon fixation to 3-phosphoglycerate by RuBisCO. Sixteen thousand species of plants use CAM. Cyanobacteria possess carboxysomes, which increase the concentration of around RuBisCO to increase the rate of photosynthesis. An enzyme, carbonic anhydrase, located within the carboxysome releases CO from the dissolved hydrocarbonate ions (HCO). Before the CO diffuses out it is quickly sponged up by RuBisCO, which is concentrated within the carboxysomes. HCO ions are made from CO outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the