The process of photosynthesis in $\mathrm{C}_4$-plants and CAM (Crassulacean Acid Metabolism) is same. But instead of spatial separation of initial PEP case fixation and final Rubisco fixation of $\mathrm{CO}_2$, 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 $\mathrm{CO}_2$ in CAM plants like $\mathrm{C}_4$-plants.