The absorbance spectrum of the brown holo-membrane and the comparison of pI values of bacteriorhodopsin solubilized from purple membrane and from brown holo-membrane |
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Authors: | Kenji Hiraki Toshiaki Hamanaka Toshio Mitsui Yuji Kito |
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Affiliation: | 1. Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560 Japan;2. Department of Biology, Faculty of Science, Osaka University, Toyonaka, Osaka 560 Japan |
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Abstract: | Brown holo-membrane was prepared by the addition of all-trans-retinal to brown apo-membrane which was isolated from Halobacterium halobium grown in the presence of nicotine. The effects of pH and NaCI concentration on the absorbance spectrum of the brown holo-membrane were investigated in comparison with those of the purple membrane. The λmax of the dark-adapted brown holo-membrane shifted from 560 to 600 nm by lowering pH. The pK value which was determined as the mid-point pH for the spectral red-shift was 5.8 in the absence of NaCl. It was lowered to 4.5 and 3.4 in 0.1 and 1 M NaCl solutions, respectively. The pK value for the brown holo-membrane was larger than the corresponding value for the purple membrane in the NaCl solution. Bacteriorhodopsins present in the purple membrane and in the brown holo-membrane were solubilized in the nonionic detergent, lauryl ester of sucrose. For both solubilized bacteriorhodopsins, the pK value of spectral red-shift was about 3.1 in water, and the pI value, determined by chromatofocusing, was about 4.6 at 22°C. |
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Keywords: | Purple membrane Brown holo-membrane Chromatofocusing Absorbance spectrum Bacteriorhodopsin (Halobacteria) BR bacteriorhodopsin BR I bacteriorhodopsin present in the purple membrane BR II bacteriorhodopsin present in the brown holo-membrane L-1690 lauryl ester of sucrose |
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