Photorespiration

Photorespiration is a plant metabolic pathway initiated when RuBisCO adds oxygen to ribulose bisphosphate instead of carbon dioxide. It consumes energy and releases carbon dioxide while salvaging the resulting products.

RuBisCO: RuBisCO is the enzyme that catalyzes carbon fixation and oxygenation of ribulose bisphosphate. Its oxygenase activity initiates photorespiration by producing phosphoglycolate.
Carbon fixation: Carbon fixation is the incorporation of inorganic carbon dioxide into organic molecules. Photorespiration diverts RuBisCO from carbon fixation and can release previously fixed carbon.
C4 carbon fixation: C4 carbon fixation concentrates carbon dioxide near RuBisCO using spatially separated steps. This adaptation suppresses photorespiration, especially in hot, bright environments.
Photosynthesis: Photosynthesis is the process by which organisms use light energy to convert inorganic carbon into organic compounds. Photorespiration occurs alongside photosynthesis and draws on intermediates from its carbon-fixation reactions.
Ribulose bisphosphate: Ribulose bisphosphate is a five-carbon sugar phosphate used by RuBisCO in carbon fixation and oxygenation. RuBisCO’s reaction with oxygen splits it into 3-phosphoglycerate and phosphoglycolate.
C3 carbon fixation: C3 carbon fixation is a pathway in which the first stable product of carbon dioxide fixation has three carbon atoms. Photorespiration is especially consequential in plants relying on this mode of carbon fixation.
CAM photosynthesis: CAM photosynthesis separates carbon dioxide uptake at night from its use during the day. Its temporal carbon storage helps limit photorespiration while conserving water.
Respiration: Respiration is cellular metabolism that releases usable energy by oxidizing organic molecules. Despite its name, photorespiration is distinct from mitochondrial respiration and does not produce ATP overall.
Phosphoglycolate: Phosphoglycolate is a two-carbon product formed when RuBisCO oxygenates ribulose bisphosphate. The pathway converts this unusable Calvin-cycle product into metabolites the plant can recover.
Oxygen: Oxygen is a reactive gas that serves as a substrate for RuBisCO’s oxygenase reaction. Its availability at the enzyme competes with carbon dioxide for RuBisCO’s active site.

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