Chloroplast membranes of the green alga Acetabularia mediterranea. II. Topography of the chloroplast membrane.

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Abstract
The localization of the chlorophyll-protein complexes inside the thylakoid membrane of A. mediterranea was determined by fractionating the chloroplast membrane with EDTA and Triton X-100, by using pronase treatment, and by labeling the surface-exposed proteins with 125I. The effects of the various treatments were established by electrophoresis of the solubilized membrane fractions and EM. After EDTA and pronase treatment, the membrane structure was still intact. Only the 2 chlorophyll-protein complexes of 67,000 and 125,000 daltons and an additional polypeptide of 35,000 daltons are part of this membrane fraction. More than 50 polypeptides were found in the membrane before the EDTA and pronase treatment. The 125,000 dalton complex seems to be buried inside the lipid layer. The 23,000 dalton subunit of the 67,000 dalton complex is largely exposed to the surface of the EDTA-insoluble membrane and only the chlorophyll-binding subunit of 21,500 daltons is buried inside the lipid layer.