A quantum-chemical study of transition structures for enolization and oxygenation steps catalyzed by rubisco: on the role of magnesium and carbamylated Lys-201 in opening oxygen capture channel

Enolization and subsequent oxygenation transition structures are calculated as saddle points for a minimal model, isolated and with a magnesium coordination sphere. Only the magnesium-embedded enolization transition structure has a substrate dihedral O2–C2–C3–O3 of around −58°. This conformation is enforced by the carbamylated-lysine via H-bonding to O3 thereby creating a necessary condition to produce spin scramble during oxygen fixation. The calculations suggest all bond breaking and making related to intra- molecular hydrogen shuttle processes are homolytic. This would explain the electronic activation of the C2-center to carry on either O2 or CO2 fixation depending upon which species is in the neighborhood.