期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1987
卷号：84
期号：15
页码：5221-5225
DOI：10.1073/pnas.84.15.5221
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We have obtained room-temperature transient infrared difference spectra of the M412 photoproduct of bacteriorhodopsin (bR) by using a "rapid-sweep" Fourier-transform infrared (FT-IR) technique that permits the collection of an entire spectrum (extending from 1000 to 2000 cm-1 with 8-cm-1 resolution) in 5 ms. These spectra exhibit less than 10(-4) absorbance unit of noise, even utilizing wet samples containing approximately 10 pmol of bR in the measuring beam. The bR----M transient difference spectrum is similar to FT-IR difference spectra previously obtained under conditions where M decay was blocked (low temperature or low humidity). In particular, the transient spectrum exhibits a set of vibrational difference bands that were previously attributed to protonation changes of several tyrosine residues on the basis of isotopic derivative spectra of M at low temperature. Our rapid-sweep FT-IR spectra demonstrate that these tyrosine/tyrosinate bands are also present under more physiological conditions. Despite the overall similarity to the low-temperature and low-humidity spectra, the room-temperature bR----M transient difference spectrum shows significant additional features in the amide I and amide II regions. These features' presence suggests that a small alteration of the protein backbone accompanies M formation under physiological conditions and that this conformational change is inhibited in the absence of liquid water.
