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 coordi nation sphere. Only the magnesium-embedded enolization transition structure has a substrate dihedral O2-C2-C3-O3 of around - 58 degrees. This conforma tion is enforced by the carbamylated-lysine via H-bonding to O3 thereby cre ating a necessary condition to produce spin scramble during oxygen fixation . The calculations suggest all bond breaking and making related to intra- m olecular hydrogen shuttle processes are homolytic. This would explain the e lectronic activation of the C2-center to carry on either O-2 or CO2 fixatio n depending upon which species is in the neighborhood. (C) 2000 Elsevier Sc ience B.V. All rights reserved.