In photorespiration, what is the function of RuBisCO?

RuBisCO is the most plentiful enzyme present in the world. The full form of RuBisCO is Ribulose-1,5-bisphosphate carboxylase oxygenase. It catalyses the carboxylation of RuBP, which is the fixation of CO2 in the synthesis of glucose in the Calvin cycle. It also has an affinity for O2 and shows oxygenase activity during photorespiration.

The function of RuBisCo in photorespiration

Photorespiration is a respiratory process in many higher plants

  • In photorespiration, RuBisCO catalyses the oxygenation of RuBP to one molecule of PGA and phosphoglycolate.
  • PGA move into the Calvin cycle, while the phosphoglycolate is hydrolysed to form glycolate.
  • Glycolate then passes to the peroxisome, where it is oxidised to glyoxylate, which in turn is converted to form glycine.
  • Glycine enters the mitochondria where two molecules of glycine condense to form a molecule of serine with the release of CO2 and ammonia.
  • Serine moves back to the peroxisome, where it is deaminated to glycerate, which passes to the chloroplast for the synthesis of photosynthetic product and photorespiration, thus completing the cycle.

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