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, LHCIIβ. This and a comparison of the amino acid and pigment compositions of the apoproteins of the LCHI and LCHIIβ chlorophyll‐proteins indicate that these are two distinct but similar chlorophyll‐proteins.