A Novel Method for the Visualization of Outer Surfaces from Stacked Regions of Thylakoid Membranes
Freeze-etch studies of thylakoid membranes reveal outer and inner surfaces that are rich in structural detail. The inner surface is covered with tetrameric particles that have been associated with the extrinsic oxygen-evolving proteins of PS II1,2 and are concentrated in the stacked (grana) regions of the membrane3. The outer surface of non-stacked regions contains large particles identified as the CF1 subunit of the ATP synthase4 and smaller particles which may represent PS I. The only thylakoid surface that has not been studied in detail is the outer surface from the stacked region. In the past this surface has been inaccessible by the stacking process itself. In this paper we describe a method to expose the previously hidden outer surface. The structure of this surface is remarkably smooth, with no apparent surface particles. This striking lateral heterogeneity of the outer surface and the extreme smoothness of the stacked region suggest new restrictions on the lateral and transverse distribution of thylakoid membrane components.
KeywordsOuter Surface Thylakoid Membrane Extrinsic Protein Rhode Island 02912 Cell BioI
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