Biogenesis of chloroplast membranes: XIV. Inhomogeneity of membrane protein distribution in photosystem particles obtained from Chlamydomonas reinhardi. Y-l

Abstract

Treatment of chloroplast membranes of Chlamydomonas reinhardi with Triton-× 100 yielded membrane particles which were resolved into three bands on discontinuous sucrose gradients. One of these was enriched in the chlorophyll absorption and fluorescence properties and photosynthetic activities consistent with photosystem I enrichment, while another had the chlorophyll absorption and fluorescence properties expected to photosystem II enriched particles. The third type of particle was enriched in chlorophyll species which are probably the bulk chlorophylls of photosystem I. Analysis of the proteins of these fractions by polyacrylamide electrophoresis indicated substantial differences, the most striking being that the photosystem II particle type was greatly enriched in the major species of chloroplast membrane protein. Previous work has shown this to be an important protein controlling membrane assembly. This protein was depleted in the photosystem I particle type. We interpret this data to indicate a lack of homogeneity in the distribution of membrane proteins in the chloroplast membranes of Chlamydomonas, at the level of the two photosystems.