The acceptor of CO₂ in C₃ -plant is

The acceptor of CO₂ in the C₃ -the plant is 1, 5 ribulose biphosphate (RUBP a 5 Carbon compound).
The enzyme RuBisCO catalyzes the carboxylation of ribulose-1,5-bisphosphate, RuBP, a 5-carbon compound, by carbon dioxide (a total of 6 carbons) in a two-step reaction.
The product of the first step is an enediol-enzyme complex that can capture CO₂ or O₂. Thus, enediol-enzyme complex is the real carboxylase/oxygenase.