Photorespiration

Rubisco (Ribulose Biphosphate Carboxylase) is an allosteric enzyme involved in photosynthesis in which oxygen and carbon dioxide compete for the same binding site. If carbon dioxide levels are high, more carbon dioxide binds to rubisco and photosynthesis continues. If oxygen levels are high, however, then oxygen binds to rubisco and produces carbon dioxide and ammonia. This is wasteful since no ATP or NADPH is formed.