CATALYTIC MECHANISM OF ALDOSE REDUCTASE STUDIED BY THE COMBINED POTENTIALS OF QUANTUM-MECHANICS AND MOLECULAR MECHANICS

The catalytic reduction of D-glyceraldehyde to glycerol by aldose redu ctase has been investigated with the combined potentials of quantum me chanics (QM) and molecular mechanics (MM) to resolve the question of w hether Tyr48 or His110 serves as the proton donor during catalysis. Si te directed mutagenesis studies favor Tyr48 as the proton donor while the presence of a water channel linking the N delta 1 of His110 to the bulk solvent suggests that His110 is the proton donor. Utilizing the combined potentials of QM and MM, the binding mode of substrate D-glyc eraldehyde was investigated by optimizing the local geometry of Asp43, Lys77, Tyr48, His110 and NADPH at the active site of aldose reductase . Reaction pathways for the reduction of D-glyceraldehyde to glycerol were then constructed by treating both Tyr48 and His110 as proton dono rs. Comparison of energetics obtained from the reaction pathways sugge sts His110 to be the proton donor. Based on these findings, a reductio n mechanism of D-glyceraldehyde to glycerol is described. (C) 1998 Els evier Science B.V.