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Next: 11. Nucleic Acids Up: Elementary X-Ray Diffraction for Biologists Previous: 9. Immunochemistry

10. Membranes

The bacterium Halobacterium halobium can survive only in solutions with concentrations above 12% salt. When oxygen is in short supply, light is used as a source of energy, first by creating a gradient of hydrogen ions across the cell membrane, and then using this electrochemical gradient to make ATP. Protons are pumped out of the cell. The purple membrane, which occurs as differentiated patches with a regular structure, works as this proton pump and has been studied by diffraction techniques (X-ray and electron diffraction). One molecule of protein, molecular weight 26,000, consists of seven rods 40 Å long (presumably $\alpha$ -helices) extending through the membrane.

References (purple membrane)

1. X-ray studies of suspension in water. Blaurock, A. E. and Stoeckenius, W., Nature New Biol . 233 (1971) 152.

2. Electron diffraction and structure determination. Unwin, P. N. T. and Henderson, R., J. Mol. Biol . 94 (1975) 425; Henderson, R. and Unwin, P. N. T., Nature 257 (1975) 28.

3. Review. Henderson, R., Ann. Rev. Bioeng . 6 (1977) 87.

Other information on membranes has come from low-angle scattering experiments.

Next: 11. Nucleic Acids Up: Elementary X-Ray Diffraction for Biologists Previous: 9. Immunochemistry

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