Density-functional investigation on the mechanism of H-atom abstraction by lipoxygenase

摘要: Using experimentally calibrated density functional calculations on models of the active site soybean lipoxygenase 1 (SLO-1), insight has been obtained into coordination flexibility iron and its molecular mechanism catalysis. The ferrous form SLO-1 shows a variation in number solution that is related to weakly coordinating Asn694 ligand. From it determined weak Fe-O(694) bond associated with this due sideways tilted geometry imposed by protein. Release constraint (by altering hydrogen bonding network) leads pure six-coordinate site. In contrast, ferric enzyme stays five-coordinate. case, deprotonation coordinated water gives strong hydroxo donor cis position Asn694, weakening bond. Hence, stronger ligand reduced relative oxidized these models, reaction energy for H-atom transfer calculated be about -18 kcal/mol. observed change going from five-coordinate increases reduction potential protein adjusts optimal reactivity. Analysis electronic structure along coordinate actually corresponds proton-coupled electron (PCET). transferred does not localize proton, but tunnels directly substrate concerted proton tunneling-electron tunneling (PTET) process. covalently linked Fe-O-H-C bridge transition state lowers barrier provides an efficient superexchange pathway tunneling. thermal PTET process estimated +15 kcal/mol including zero-point corrections. This rate k(therm) approximately s(-1). comparison, can as high 2 x 10(9) s(-1) under conditions.