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oai:www.ideals.illinois.edu:2142/20207 2023-07-10 col_2142_5131 col_2142_14828 com_2142_5130 com_2142_14827 com_2142_14793 com_2142_8903

My more recent research shows that the binding of one divalent cation is directly related to the blue-to-purple transition of bacteriorhodopsin; whereas, four other divalent cation binding sites involving carboxyl groups on the bacteriorhodopsin surface do not directly affect the color change. The intrinsic pK$\sb{\rm a}$ of the binding of the special divalent cation and of the color transition is at about pH 2. The events involve the exchange of one divalent cation for two protons; I suggest that the two groups which release a proton upon binding of the divalent cation are aspartates-85 and -212 in the bacteriorhodopsin active site. Ebrey, Thomas G. Jonas, Roy Edward 2011-05-07T12:32:14Z 2011-05-07T12:32:14Z 10000-01-01 1991 This thesis is a report of cation effects on the purple membrane of Halobacterium halobium. Included are proton and divalent cation studies using purple, blue, and pink membranes and the apoprotein. The blue species of bacteriorhodopsin is produced from purple membrane at low pH or by removal of divalent cations. Studies contrasting purple and blue membranes have been quite useful for investigating the environment of retinal and the proton-pumping mechanism. I have also obtained interesting results from pink membrane, a stable photoproduct of blue membrane in red light. Experiments concerning changes involved in the light-induced formation of blue and purple membranes from pink and Ca$\sp{2+}$-pink membranes, respectively, are discussed. Fourier transform infrared spectroscopy and pH studies demonstrate in part that structural and/or protonation changes taking place during these transformations may involve four specific carboxylic amino acids which seem to be important in the bacteriorhodopsin photocycle. Pink membrane is also found to contain exclusively 9-cis retinal, an isomer not normally found in purple membrane. These results suggest a significant modification of the chromophore environment and bacteriorhodopsin active site is able to take place in deionized membrane. Initial evidence from atomic absorption, chemical modifications, pH titrations, and theoretical calculations showed that 5-6 divalent cations are physically bound to purple membrane by carboxylic amino acids. Cooperativity between binding of retinal and a portion of the divalent cations was also suggested by results such as reduced cation binding to the apomembrane and irreversible inhibition of chromophore regeneration using deionized-bleached membrane. Made available in DSpace on 2011-05-07T12:32:14Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9210852.pdf: 4777524 bytes, checksum: b6295d56331d046acc982cc845bdf664 (MD5) Previous issue date: 1991 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:42:20Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:18:24-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9210852 (UMI)AAI9210852 http://hdl.handle.net/2142/20207 eng Copyright 1991 Jonas, Roy Edward Biophysics, General Cation effects on the purple membrane of Halobacterium halobium text Biophysics and Computational Biology Biophysics University of Illinois at Urbana-Champaign Dissertation Ph.D.