Which enzyme catalyses wasteful oxygenation reaction in C₃ plants ?

RuBisCO) is characterised by the fact that its active site can bind to both CO2 and O2 – hence the name.  RuBisCO has a much greater affinity for CO2 when the CO2 : O2 is nearly equal.

When O2 levels ar ehighe than CO2, O2  binds to RuBisCO, and hence CO2 fixation is decreased. 

Here the RuBP instead of being converted to 2 molecules of PGA binds with O2 to form one molecule of phosphoglycerate and phosphoglycolate (2 Carbon) in a pathway called photorespiration