Synthesis of Alkyl Glycosides Catalyzed by β-Glycosidases in a System of Reverse Micelles

A basic possibility of enzymic synthesis of alkyl glycosides in a system of the Aerosol-OT (AOT) reverse micelles was studied. Octyl -D-galactopyranoside and octyl -D-glucopyranoside were synthesized from the corresponding sugars (lactose or glucose) and octyl alcohol under catalysis with glycolytic enzymes, -galactosidase and -glucosidase, respectively. The transglycosylation/hydrolysis ratio was shifted toward transglycosylation by using octyl alcohol, one of the substrates, as an organic solvent. The alkyl glycosides were thus obtained in one step from a hydrophilic mono- or disaccharide and a hydrophobic aliphatic alcohol. The direction of the reaction was shown to depend on the pH of aqueous solution solubilized in reverse micelles. The maximum yields were 45% and 40% for octyl galactoside and octyl glucoside, respectively; they markedly exceeded the yields of enzymic syntheses in a two-phase system reported previously.     

Oxidation of unsaturated phospholipids in membrane bilayer mixtures is accompanied by membrane fluidity changes

Steady-state and time-resolved fluorescence spectroscopy has been used to obtain information on oxidation processes and associated dynamical and structural changes in model membrane bilayers made from single unilamellar vesicles (SUV's) of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) mixed with increasing amounts of 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (SAPC). The highly unsaturated arachidonoyl chain containing four double bonds is prone to oxidation. Lipid oxidation was initiated chemically by a proper oxidant and could be followed on line via the fluorescence changes of an incorporated fluorescent lipophilic fatty acid: 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (BP-C11). The oxidation rate increases with an increasing amount of SAPC. Size measurements of different SUV's incorporated with a trace amount of a phosphatidylcholine analogue of BP-C11 using fluorescence correlation spectroscopy have demonstrated that an increase of lipid unsaturation results in smaller sized SUV's and therefore to a larger curvature of the outer bilayer leaflet. This suggests that the lipid-lipid spacing has increased and that the unsaturated fatty acyl chains are better accessible for the oxidant. Oxidation results in some characteristic physical changes in membrane dynamics and structure, as indicated by the use of specific fluorescence probes. Fluorescence measurements of both dipyrenyl- and diphenylhexatriene-labelled PC introduced in non-oxidised and oxidised DOPC-SAPC membranes clearly show that the microfluidity (local fluidity at the very site of the probes) significantly decreases when the oxidised SAPC content increases in the lipid mixture. A similar effect is observed from the lateral diffusion experiments using monopyrenyl PC in the same membrane systems: the lateral diffusion is distinctly slower in oxidised membranes.