The quantasome as seen in a two-dimensional crystalline array is 185 A long, 155 A wide, and 100 A thick. The surface of the quantasome appears to contain four or more subunits. The molecular weight, determined from volume and density measurements, is 2 x 10(6) This is twice the minimum molecular weight calculated from the manganese content and corresponds to a chlorophyll content of 230 chlorophyll molecules per quantasome.

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A comparative study of peptide composition and freeze-fracture morphology of chloroplast membranes from a chlorophyll b-less mutant and a normal barley plant (Hordeum vulgare L.) is reported in this work. Using a high resolution, discontinuous sodium dodecyl sulfate acrylamide gel electrophoretic system, we show that the mutant chloroplast membranes not onlv completely lack the 25-kilodalton peak, which accounts for about 18% of the chloroplast membrane protein in the normal plant, but also exhibit gross reduction in other components at 27.5-and 20-kilodalton regions. In this paper we explore the peptide composition of mutant chloroplast membranes in greater detail than reported previously. So that our results are comparable to previous studies, we analyzed the mutant and wild-type membranes by polyacrylamide disc gel electrophoresis. These preparations were then further analyzed using a high resolution SDS-acrylamide slab gel electrophoretic technique.A freeze-fracture study of the photosynthetic membranes of both the Chl b-less mutant and the wild type is also presented. This study was prompted, in part, by recent observations in our laboratory (19) that in spinach the peaks in the 25 kD3 region, which may be assumed homologous with those in barley, are associated with the inner fracture face (B) of the membrane which is the site of the large particles. If a similar correlation holds for barley chloroplasts, one would expect that the mutant chloroplast, lacking this group of polypeptides, might exhibit some modification of the large B-face particles. MATERIALS AND METHODS

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