The primary carbon assimilatory enzyme in C4 is

C4 cycle is referred to as the β-carboxylation pathway and cooperative photosynthesis.
The 4-carbon oxaloacetic acid is the first stable compound of the Hatch and Slack cycle. PEPCase i.e. Phosphophoenolpyruvate carboxylase is an enzyme involved in C4 pathways and is the primary carbon assimilatory enzyme in C4.