Light-Harvesting Chlorophyll-Proteins of Barley Photosystem I

Abstract

Photosynthetic membranes of higher plants contain two distinct types of reaction centres - photosystem I (PSI) and photosystem II (PSII). The major chlorophyll-protein contains chlorophyll (Chl) a and b and functions as a light-harvesting antenna complex for PSII, and is therefore called LHCII. While both PSI and PSII reaction centres contain only Chl a, there is much more Chl associated with the PSI reaction centre chlorophyll-protein and it was only quite recently that a PSI-specific light-harvesting antenna (LHCI) was isolated. Its existence as a separate chlorophyll-protein was first predicted on the basis of the difference in the Chl:P700 ratio of a PSI “core” preparation compared with that of the starting material (Mullet et al. 1980). It was first isolated as a Chl-containing complex by Haworth et al. (1983), who showed that it contained Chi b (Chl a/b ratio = 3.7), fluoresced at 730 nm and consisted of a group of polypeptides of 19–24 kD.