In peroxisomes, glycolate oxidase catalyzes the oxidation of glycolate by O2, producing H2O2 and glyoxylate (see Table 8.2, reaction 3). (...) Subsequently, glutamine and 2-oxoglutarate are substrates of ferredoxin-dependent glutamate synthase (GOGAT) for the production of two molecules of glutamate (see Table 8.2, reaction 12). The reassimilation of NH4+ into the photorespiratory cycle restores glutamate for the action of the peroxisomal glutamate:glyoxylate aminotransferase in the conversion of glyoxylate to glycine (see Table 8.2, reaction 5).
In the oxygen cycle, rubisco and glycolate oxidase catalyze the incorporation of two molecules of O2 each (eight oxygen atoms) when two molecules of ribulose 1,5-bisphosphate enter the C2 oxidative photosynthetic carbon cycle (see Table 8.2, reactions 1 and 3). However, catalase releases one molecule of O2 from two molecules of H2O2 (two oxygen atoms) (see Table 8.2, reaction 4).
For salvaging two molecules of 2-phosphoglycolate by conversion to one molecule of 3-phosphoglycerate, photophosphorylation provides one molecule of ATP necessary for the transformation of glycerate to 3-phosphoglycerate (see Table 8.2, reaction 10), while the consumption of NADH by hydroxypyruvate reductase (see Table 8.2, reaction 9) is counterbalanced by its production by glycine decarboxylase (see Table 8.2, reaction 6). In photorespiration, nitrogen:
enters into the peroxisome through the transamination step catalyzed by the glutamate:glyoxylate aminotransferase (two nitrogen atoms) (see Table 8.2, reaction 5), and
leaves the peroxisome (1) as NH4+ (one nitrogen atom), in the reaction catalyzed by the glycine decarboxylase-serine hydroxymethyltransferase complex (see Table 8.2, reactions 6 and 7) and (2) in the transamination step catalyzed by serine:2-oxoglutarate aminotransferase (one nitrogen atom) (see Table 8.2, reaction 12).
"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.
