フミン物質とリポソームとの相互作用

抄録

The effects of marine and terrestrial humic substances on the K⁺-permeability of lipid bilayer of dimyristoyl phosphatidylcholine (DMPC) liposomes were investigated for their physiological activity on biological membranes. Commercial humic acid and humic and fulvic acids extracted from soil and marine sediment were used for the experiment.
Potassium ions inside liposomes were released through the DMPC bilayer following the addition of humic acid. The effect of humic acid was conspicuous above the phase transition temperature of DMPC. Humic acids containing many carboxyl groups but few phenolic and alcoholic hydroxyl groups had little effect on the K⁺-permeability of the bilayer. From the relation between the K⁺-permeability and the degree of humification determined by optical spectroscopy, humic acids humified to a lesser extent were found to interact strongly with liposomes. The K⁺-permeability enhancing effect was stronger in the case of highly aliphatic marine humic acids than highly aromatic terrestrial acids. Hydrophilic fulvic acid exerted virtually no effect on K⁺-permeability. The hydrophobic chain of the acid would thus appear to be incorporated into the hydrophobic core of lipid bilayer, enhancing the fluidity of the lipid.
The lower molecular weight fractions of marine humic acids promoted K⁺-release more than the original humic acids. The commercial humic acids with smaller molecular size affected strongly K⁺-permeability compared to marine humic acids having essentially the same humification and functional group content. This molecular size effect indicates the rates of adsorption of humic acid molecules onto and their incorporation into the lipid bilayer to possibly contribute to interactions with liposomes.