Coenzyme model reaction in lipid bilayers

Coenzyme model reactions, such as the H⁻ (H⁺ + 2e⁻) transfer from NADH models to triphenyl methane dyes, were investigated in the presence of lipid bilayers, for example, -α-dimyristoyl phosphatidyl choline and egg yolk lecithin. In the temperature dependence of the acceleration effect by the lipid bilayer, discontinuous points were observed, corresponding to the phase transition point such as gel-liquid crystal (T_c) or the segregation point (T_s). The T_c and T_s values of the bilayers varied with the reactant as a result of the difference of perturbing effect on the structure of the bilayers. The pressure effect on the transition point was also studied. Transition points such as T_c or T_s became higher with increasing pressure, and dT_c/dP or dT_s/dP was different for various bilayers. In the gel phase of the membrane, stereospecific reduction of malachite green was observed by chiral nicotinamide: the difference in the catalytic effect on the reduction rate between (R)- and (S)-dihydronicotinamides was larger in the gel phase than that in the liquid crystal phase or in the phase separated state, which suggests that the gel-state molecule can recognize the molecular structure better than the liquid-crystal state molecule.