PEPC is particularly important in C4 and CAM plants. These plants need PEPC for photosynthetic fixation by ribulosebisphosphate carboxylase and the Calvin Cycle of carbon dioxide (Rustin, Meyer, Wedding, 1988). PEPC in plants is very similar to that in E. coli in that many residues are highly conserved in all PEPCs identified. The mechanism of both structures are slightly different in that the PEPC roles in both are different. In both E. coli and C4 plants, there exists an active and inactive form of PEPC and three binding domains seem to be present. The binding sites in plants are referred to as the phosphoenolpyruvate binding site or catalytic site, a malate binding site or inhibition site, and Glucose-6-P binding site or activation site (Rustin, Meyer, Wedding, 1988). PEPC in E. coli also has a activation site but the location still remains to be known. However, acetyl-coenzyme A, fructose 1,6-bisphosphate, GTP, and long-chain fatty acids are all activators of E.coli PEPC (Yano, 1997). In CAM plants, PEPC is activated at night and inactivated during the day. When PEPC is activated it functions in the tetrameric form and when PEPC is inactivated it dissociates into two non-functional dimers. The inactive/active forms are due to the binding of the allosteric effector L-malate, oligomerization, and /or phosphorylation. The phosphorylated form of the enzyme exists during the daytime, while the nonphosphorylated form exists at night. The phosphorylation occurs at a serine residue located at the N-teriminus of the beta barel. The N-termini not only influences the phosphorylation status of the enzyme and its sensitivity to malate, but it influences the affinities of the active site for its substrates.

The binding of G-6-P to PEPC in C4 and CAM plants is essential to the activation of PEPC. The binding of G-6-P to the activation site increases the affinity of phosphoenolpyruvate to the catalytic site by lowering the K_m of PEPC for phosphoenolpyruvate from 0.2 to 0.01mM (Rustin, Meyer, Wedding, 1988). Divalent metal ions, mainly Mg⁺², are also essential activators of all PEPCs identified (Tovar-Mendez et. al, 1998). Mg⁺² stabilizes the reaction catalyzed by PEPC. Mg⁺² is thought to either form a binary complex with PEP before it binds to PEPC. The free species, meaning free phosphoenolpyruvate and Mg⁺², do not bind to the active site. Only in the presence of the activators and a raise in pH does the free species bind to the active site. The cystolic concentration of free PEP is around 10-fold to that of Mg-PEP indicating the formation of the active site-MgPEP complex is favored over the formation of the active-site free PEP complex (Tovar-Mendez et. al, 1998). This is evidence that the MgPEP complex does form.

As stated earlier the complete mechanism of the PEPC is not entirely known and the information that is known is fairly recent. So, there is room for lots of research on the function of PEPC. We do know that PEPC is needed and essential for metabolic reactions. From Yano (1988), a high expression of the mutant PEPC in cells of bacterial strains for amino acid fermentation may augment the cells productivity. CAM plants of the desert and the tropics use PEPC to eliminate the lose of water from obtaining carbon dioxide from the hot, humid air of the daytime. In this case, PEPC functions at nighttime when the air is cooler thus the evaporation rate is lower. We, as humans, may not use PEPC but it doesn't mean that it isn't biologically significant. For instance many cures for diseases are found in plants dwelling in the rainforest, and if these plants would all of a sudden gain a nonfunctional PEPC extinction of these plants could occur, leaving us out of luck for a cure.