| Abstract: | A photosystem I (PS I) holocomplex was obtained from barley by ultracentrifugation of PS I-enriched stroma lamellae on sucrose gradients. Further solubilization with glycosidic surfactants followed by Deriphat-poly-acrylamide gel electrophoresis (PAGE) fractionated the holocomplex into its core complex (CC I) and individual light-harvesting I (LHC I) pigment-protein subcomplexes. The LHC I contains chlorophyll a, all of the chlorophyll A of PS I and xanthophylls but no carotenes. Sodium dodecylsulfate PAGE analysis of the subcomplexes shows that barley LHC I is composed of at least five apoproteins having sizes between 11 and 24 kDa. Isolation of a 17 kDa LHC Ic component by Deriphat-PAGE shows it to be a photosynthetic pigment-protein. Room-temperature absorption spectra indicate that LHC Ic is enriched in chlorophyll a in comparison to the LHC Ia and Ib components. The LHC Ic apoprotein is shown to be distinct from the subunit III and IV polypeptides of CC I. Analysis of PS I fractions obtained from sucrose gradients as well as from Deriphat-PAGE indicates that in higher plants an oligomeric structure of the PS I entity exists in vitro. |
