Photorespiration – Damage Repair Pathway of the Calvin–Benson Cycle

Abstract The photorespiratory repair pathway is an indispensable component of the photosynthetic CO2assimilation apparatus and a major highway of plant primary metabolism. The photorespiratory pathway interacts with the tricarboxylic acid (TCA) cycle in at least three ways: synthesis of 2‐oxoglutarate (2OG) for nitrogen metabolism, inhibition of TCA cycle enzymes by ammonia and NADH, and competition for NAD+. The preference given to NADH oxidation interlinks photorespiratory glycine oxidation with oxidative phosphorylation to provide adenosine triphosphate (ATP) to the cytosol. Use of water for photosynthesis, together with the generation of molecular oxygen, triggered a major side reaction at the key CO2fixation enzyme ribulose 1,5‐bisphosphate carboxylase (Rubisco): addition of dioxygen cleaves the CO2acceptor molecule ribulose 1,5‐bisphosphate (RuBP), generating the powerful enzyme inhibitor glycolate 2‐phosphate (2PG). Central for photorespiration is the conversion of the two‐carbon skeleton of glycolate into a three‐carbon skeleton that is compatible with the Calvin‐Benson cycle.