photorespiration
photorespiration
A light-dependent catabolic process occurring concomitantly with photosynthesis in plants (especially C3 plants) whereby dioxygen (O2) is consumed and carbon dioxide (CO2) is evolved. The substrate is glycolate formed in large quantities in chloroplasts from 2-phosphoglycolate generated from ribulose 1,5-bisphosphate by the action of ribulose-bisphosphate carboxylase; the glycolate enters the peroxisomes where it is converted by glycolate oxidase to glyoxylate which undergoes transamination to glycine. This then passes into the mitochondria where it is decarboxylated forming one molecule of serine for every two molecules of glycine. This pathway also exists in photosynthetic bacteria.