On the importance of being zwitterionic: enzymatic catalysis of decarboxylation and deprotonation of cationic carbon

摘要: Carbanion ylides are strongly stabilized by electrostatic interactions between opposing charges at neighboring atoms and this stabilizing interaction increases with decreasing dielectric constant of the medium through which interact. Consequently, there is a large increase in thermodynamic driving force, reaction medium, for deprotonation cationic carbon acids decarboxylation to form related ylides. This favors catalysis formation unstable enzyme active sites low constant. A brief survey enzymes that catalyze reactions shows generally occurs substrates bound deep pocket on protein, an apparent much lower than solvent water. In several cases, proton transfer catalytic residue relatively weakly solvated We suggest strong advantage evolution protein catalysts utilize basic side chains easily buried nonpolar favorable zwitterion formation.