ENZYMATICALLY GENERATED ELECTRON-EXCITED SPECIES INCREASE THE MEMBRANE ORDER-PARAMETER WITHOUT CHANGING THE ROTATIONAL RELAXATION-TIME OF TMA-DPH

The effect of enzymically generated triplet acetone produced from 60 m mol/l 2-methylpropanal (MPAL) in the presence of 2 mu mol/l horseradis h peroxidase on the properties of artificial unilamellar liposomes was studied. The concentration of malondialdehyde, membrane lateral press ure (membrane order parameter), lifetime distribution of the excited s tate of TMA-DPH incorporated into liposomes, and rotational relaxation time of TMA-DPH were determined. The concentration of MDA increased w ith the MPAL concentration, and the membrane lateral pressure increase d linearly with the concentration of MDA. The mean lifetime values cha nged (p < 0.01) as did the limiting anisotropy (p < 0.005), the widths of the main peak of the lifetime distribution and the rotational rela xation time remaining unchanged. This indicates that there is no signi ficant difference between the widths and rotational relaxation times i n the control and triplet-acetone-treated sample: i.e. peroxidation by MPAL increased the lipid order of the bilayer but the effect of neigh boring lipid molecules on the dynamics of the probe was negligible.