Synthetic compounds to probe molecular events in bacteriorhodopsin.
Item
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Title
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Synthetic compounds to probe molecular events in bacteriorhodopsin.
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Identifier
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AAI9405511
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identifier
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9405511
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Creator
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Chen, Liang.
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Contributor
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Adviser: Valeria Balogh-Nair
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Date
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1993
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic | Chemistry, Biochemistry
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Abstract
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Bacteriorhodopsin (bR), the only protein species of the purple memberane of Halobacterium halobium, functions as a light-driven proton pump. It contains all-trans retinal as a chromophore, which is bound to a lysine-216 residue via a protonated Schiff base linkage. Absorption of light as energy by all-trans retinal in bR initiates a cyclic photoreaction, during which a proton is actively translocated across the membrane.;The presence of all-trans retinal in this protein provides a means of investigating the structure of the active sites and the mechanism of action. A method for proving the structure of protein is through the use of photoaffinity labeling. Aryl azide, trifloromethylphenyl diazirine, and diazoacetoxy retinals have been synthesized for this purpose. Incubation of these retinals with bacterio-opsin yielded pigments absorbing maximally at 472, 465, and 540 nm, respectively. The method of finding labeled site(s) in bR by cross-linking using trifluoromethylphenyl diazirine analog is being used by Dr. Crouch's group in the Eye Institute, Medical University of South Carolina.;The ring-truncated retinal containing spacer arm with seven carbons has also been synthesized for rapid preliminary testing of binding ability to the retinal binding site of opsin. Binding studies with this analog and bacterio-opsin showed an absorption pigment generated with an absorption maximum at 480 nm. The formation of the series of pigments from above analog retinals indicated that the ring binding site in nature bR is flexible enough.;By application of the Nuclear Overhauser Effect (NOE) to conformational analysis, we have found evidence that ring-truncated analog retinals can generate different stable conformations. The conformational equilibrium, 6-s-cis and 6-s-trans, can also exist in each conformation. Moreover, we have found that a stabilizing interaction between lone pairs and the electrons of the {dollar}\pi{dollar} system of the polyene chain may occur in ring-truncated analogs in our case. This effect has been observed when acid chlorides were employed for esterification of ring-truncated analogs. Apparently these analogs are found two conformational isomers in the pure state, and another one can exist in solution as well. The 1-diazoacetoxy retinal can lead to four conformations as indicated by four individual diazo protons. Finally, the stereochemistry of ring-truncated analog retinals has been established and a detailed picture of the molecule has emerged.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
