Aggregation behavior of synthetic peptide lipids with arginine in aqueous solution and construction of a vitamin B₁₂ artificial enzyme

A novel amphiphile (N⁺C₅Arg2C₁₆) having an arginine residue and a dihexadecyl moiety for the double-chain segment was synthesized, and it's aggregate behavior was examined by electron microscopy, differential scanning calorimetry, and fluorescence polarization measurements. The hybrid vesicles formed with an alanine lipid, N⁺C₅Ala2C₁₆, and an arginine lipid, N⁺C₅Arg2C₁₆, are morphologically very stable. Hydrophobic vitamin B₁₂ derivatives, which have carboxylic ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B₁₂, were incorporated into the single-walled vesicles of N⁺C₅Ala2C₁₆ and N⁺C₅Arg2C₁₆ to construct an artificial holoenzyme with vitamin B₁₂ activity. In these hybrid bilayer vesicles, the enzyme mimicking reaction of methylmalonyl-CoA mutase, which is 1,2-migration of carboxylic ester group on an axial ligand of the cobalt, has been enhanced by microenvironmental effects. (C) 2000 Elsevier Science B.V.