Studies on the absorption spectra of chlorophyll a in aqueous dispersions of lipids from the photosynthetic membranes

Abstract

The absorption spectra of chlorophyll a were studied in aqueous dispersions of four major lipid components present in the thylakoid membranes. Chlorophyll a in aqueous dispersions of uncharged galactolipids revealed two absorption bands, at 670 and 745 nm, when the molecular ratio of chlorophyll to lipid was higher than 0.2. The latter band may be due to the formation of microcrystals of chlorophyll a. Chlorophyll a in aqueous dispersions of negatively charged lipids revealed a single absorption band at 670 nm. However, chlorophyll a was decomposed during measurement in these lipid dispersions. The absorption spectra of chlorophyll a in aqueous dispersions of mixture of galactolipid and charged lipid were apparently similar to those of chlorophyll a in the charged lipid dispersion. Chlorophyll a, however, was not decomposed in these aqueous dispersions of lipid mixtures. It is concluded that the presence of both galactolipid and charged lipid are necessary to reconstruct the state of chlorophyll a dissolved in the lipid phase in the thylakoid membranes. The red absorption band of chlorophyll a in the reconstructed system composed of chlorophyll a, charged and uncharged lipids, appeared at 670 nm with a half bandwidth of 22 nm. Analysis of the absorption spectrum in the fourth derivative and the curve-fitting methods indicated that the red band was composed mainly of a single band with a peak at 670–671 nm.