Essentiality of the small subunit (B) in the catalysis of RuBP carboxylase/oxygenase is not related to substrate-binding in the large subunit (A).
The small subunit (B) of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase from Aphanothece halophytica is absolutely required for the catalysis, but depletion of subunit B does not significantly affect the formation of the quaternary complex-[enzyme.activator CO2.Mg.carboxyarabinitol bisphosphate] in the catalytic core. The inhibition of RuBP carboxylase activity by the reaction of the epsilon-amino group of a lysine in the RuBP-binding site with pyridoxal 5-P is the same whether subunit B is added to the catalytic core before or after the inactivating reaction. The function of subunit B is not related to the substrate binding.
D001665:Binding Sites; D002245:Carbon Dioxide / Q000032:analysis; D002250:Carbon Radioisotopes; D000458:Cyanobacteria / Q000201:enzymology*; D046911:Macromolecular Substances; D011485:Protein Binding; D011732:Pyridoxal Phosphate / Q000032:analysis; D012273:Ribulose-Bisphosphate Carboxylase / Q000302:isolation & purification / Q000378:metabolism*
D002250:Carbon Radioisotopes; D046911:Macromolecular Substances; D002245:Carbon Dioxide; D011732:Pyridoxal Phosphate; D012273:Ribulose-Bisphosphate Carboxylase