The effect of the marine humic acid on lipid bilayer liposomes was studied to evaluate the physiological activity of humic acids to the biological membrane.
A marine humic acid extracted from a sediment of Suruga Bay was used. Dimyristoylphosphatidylcholine (DMPC) was treated by the alcohol method to prepare the liposome solution, then was subjected to gel permeation chromatography on a Sepharose 4 B column.
Potassium ion was released when humic acid was added to liposomes containing potassium ion at 30°C. A valinomycine impregnated ion selective electrode was used for detection of the ion. The high concentration of humic acid caused a rapid release of the ion. The effect was markedly observed above the phase transition temperature.
The liposome solution incubated with the humic acid at 30°C for more than 48 h showed an increase in its turbidity ; which was ascribed to the fusion of liposomes. At the ratio of the humic acid concentration to the DMPC concentration 510, the fusion was seemed to be inhibited. The fusion was considerably slow compared to the other two interactions.
The phase transition temperature of DMPC liposomes was determined by means of a fluorescent probe. Liposomes with the fluorescent probe were incubated with the humic acid for 1 h at 30°C and the fluorescence intensity was measured. Above 1 ppm of the humic acid shifted the phase transition to lower temperature by 2°C and less than 1 ppm caused the effect proportional to the concentration.
These results indicate that the humic acid interacts with liposomes to change the surface of the membrane and to increase the liquidity of the lipid.
抄録全体を表示