Purification and characterization of a light-harvesting chlorophyll-a/b-protein of photosystem I of Lemna gibba.

The photosystem I (PSI) complex of Lemna gibba, isolated by deriphat/polyacrylamide gel electrophoresis of thylakoids solubilized in glycosidic surfactants, has been fractionated into its two chlorophyll-protein complexes: a core component (CCI) and a light-harvesting component (LHCI), using either non-denaturing gel electrophoresis or ion-exchange chromatography/sucrose gradient centrifugation. Both methods yielded an LHCI component that contained only one apoprotein of approximately 20 kDa. All the chlorophyll b and lutein of the PSI complex is associated with this LHCI preparation. The chlorophyll a/b ratio of this chlorophyll-protein is 2.5, and lutein is essentially the only carotenoid present. While the purified LHCI from Lemna cross-reacts with antibodies raised against spinach LHCPIb of Lam et al. [FEBS Lett. 168, 10-14 (1984)], no cross-reactivity occurred between it and the major light-harvesting chlorophyll-a/b-protein of PSII, LHCII beta. This and a comparison of the amino acid and pigment compositions of the apoproteins of the LHCI and LHCII beta chlorophyll-proteins indicate that these are two distinct but similar chlorophyll-proteins.