The oxygenation activity of RuBisCO enzyme in photorespiration leads to the formation of :

In C3 plants some O2 does bind to RuBisCO, and hence CO2 fixation is decreased. Oxygenation activity of RuBisCO produces one molecule of 3C compound PGA, and one molecule of 2C compound phosphoglycolate. During the carboxylation step of Calvin cycle, RuBP combines with CO2 to form 2 molecules of 3PGA (3C), which is catalysed by RuBisCO.