Circular dichroism study of membrane dynamics. Effects of carboxymethyl-chitin.

The circular dichroism (CD) active phospholipid bis(4'-n-octanoxyazobenzene-4-carboxyl)-L-alpha-phosphatidylcholin e (CDPC) was used to study the effects of carboxymethyl-chitin (CM-chitin) on the membrane dynamics. For this purpose, CD and electronic spectra were observed for a mixture of CM-chitin and liposomes composed of CDPC and egg lecithin (EPC) (50% CDPC-EPC-liposomes), and for a mixture of CM-chitin, 50% CDPC-EPC-liposomes, and EPC-liposomes. CM-chitin at concentrations higher than ca. 10(-5) M induced the increase of absorbance at 600 nm synchronized with the dilution of CDPC in 50% CDPC-EPC-liposomes by EPC matrix, indicating that CM-chitin induces the fusion among a few liposomes and/or the lipid transfer through the transient liposome fusion. Temperature dependent CD spectra of a mixture of the 50% CDCP-EPC-liposomes and CM-chitin suggested that even high concentration of CM-chitin has no significant perturbation of the lipid organization in the membranes. The effects of CM-chitin on the leakage of [3H]sucrose from the EPC-liposomes were also studied. By the presence of 5 X 10(-6) M CM-chitin, the half-life for leakage of [3H]sucrose in plasma was increased by 4 times. This effect of CM-chitin was reduced by chitinase, while no effect was observed with lysozyme, suggesting that CM-chitin molecules are adsorbed on the liposome surface and stabilize the liposomes against the plasma proteins.