The process of photosynthesis in $C _{4}$-plants and CAM (Crassulacean Acid Metabolism) is same. But instead of spatial separation of initial PEP case fixation and final Rubisco fixation of $CO _{2}$, the two steps occur in same cell but at different times, night and day, eg, Opuntia, pineapple, Vanilla. PEP (Phosphoenol Pyruvate) is the first acceptor of $CO _{2}$ in CAM plants like $C _{4}$-plants.