Catalytic Efficiency of Functionalized Vesicles in the Transamination of Pyridoxal-5'-phosphate with a Hydrophobic Amino Acid

Article abstract of DOI:10.1246/bcsj.55.3004

The transamination reaction of pyridoxal-5'-phosphate (PLP) with N-dodecyl-L-alaninamide (AlaC12) was investigated in an aqueous phosphate-borate buffer at pH 7.0, μ 0.10 (KCl), and 30.0+/-0.1 deg C in the presence of single-walled vesicles of N,N-ditetradecyl-N^α-(6-trimethylammoniohexanoyl)-L-histidinamide bromide (N⁺C5His2C14).The electrostatic and hydrophobic interactions between the vesicles and the reactants resulted in incorporation of PLP and AlaC12 into polar and hydrophobic domains of the vesicles, respectively, in the Schiff-base formation process.The isomerization of the aldimine Schiff-base to the correspeonding ketimine Schiff-base was confirmed to be the rate-determining step in the transamination process.The reaction site in the vesicular system was found to be equivalent in polarity to dioxane-water (7:3 v/v).However, the overall reaction rate in the vesicles was enhanced 230-fold relative to that in dioxane-water (7:3 v/v).A hydrophobic and suitably polar microenvironment constructed at the reaction site is responsible for such a marked rate-enhancement.In addition, each vesicle of N⁺C5His2C14 provided functional (imidazolyl) groups in its hydrogen-belt domain to catalyze the intramolecular prototropic shift to yield the ketimine Schiff-base.The microenvironmental effects of molecular assemblies of N,N-ditetradecyl-N^α-(6-trimethylammoniohexanoyl)-L-alaninamide bromide and CTAB on the overall transamination were also discussed.