The sites for catalysis and activation of ribulosebisphosphate carboxylase share a common domain

The complexation of ribulosebiphosphate carboxylase with CO 2, Mg 2+, and carboxyarabinitol bisphosphate (CABP) to produce the quaternary enzyme-carbamate-Mg 2+-CABP complex closely mimics the formation of the catalytically competent enzymecarbamate-Mg 2+-3-keto-CABP form during enzymatic catalysis. Quaternary complexes were prepared with various metals (Mg 2+, Cd 2+, Mn 2+, Co 2+, and Ni 2+) and with specifically 13C-enriched ligands. 31P and 13C NMR studies of these complexes demonstrate that the activator CO 2 site (carbamate site), the metal binding site, and the substrate binding site are contiguous. It follows that both the carboxylase and oxygenase activities of this bifunctional enzyme are influenced by the structures of the catalytic and activation sites.