is its purpose in photosynthesis
Ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) is crucial in the regulation of photosynthesis in fully-hydrated leaves of the C4 species Flaveria bidentis (), but the importance of this most abundant of leaf proteins in the limitation of C4 photosynthesis under drought conditions is not well understood. suggested that, in C3 plants, Rubisco capacity was of little importance in the drought-induced limitation of photosynthesis, whilst decreased capacity for RuBP regeneration—possibly as a result of decreased ATP synthesis or impaired Calvin cycle enzyme activities ()—would constitute a major metabolic limitation. However, decreased activity and/or quantity of Rubisco has been observed in several different C3 and C4 species exposed to water deficit (; ; ; ; ; ; ; ; .
Ribulose 1,5-bisphosphate - Wikipedia
Rubisco activase removes inhibitors from carbamylated catalytic sites and facilitates the removal of RuBP bound to non-carbamylated sites. Rubisco activase requires ATP for activation of Rubisco but is inhibited by ADP (). If the decreased capacity for regeneration of RuBP under drought is a consequence of decreased ATP synthesis, a further consequence could be more Rubisco-bound inhibitors and fewer carbamylated Rubisco catalytic sites (; ) – both resulting from the decline in activase activity caused by a fall in the ratio ATP/ADP. Inactivation of Rubisco catalytic sites with increasing water deficit will decrease both carboxylation and oxygenation and, therefore, photosynthesis and photorespiration, as previously predicted by the modelling of carbon assimilation under drought ().
Rubisco, formally known as ribulose‐1,5‐bisphosphate (RuBP) carboxylase/oxygenase, is the chloroplast enzyme that assimilates atmospheric carbon dioxide during photosynthesis by combining it with RuBP to form two molecules of phosphoglycerate. However, Rubisco allows oxygen to react with RuBP in addition to carbon dioxide, producing phosphoglycolate, and thereby also initiates the process known as photorespiration. Genetic modification to overcome the limitations of Rubisco would have great agronomic importance.