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：1977
卷号：74
期号：8
页码：3119-3123
DOI：10.1073/pnas.74.8.3119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Picosecond studies of rhodopsin in low-temperature glasses have been carried out in order to observe directly the risetime of prelumirhodopsin, the first intermediate in the visual pathway. Only at 20 K or below can the risetime of this intermediate be resolved and even at 4 K it is astoundingly rapid, about 36 psec. An examination of the Arrhenius dependence on temperature of the rate of formation of prelumirhodopsin shows a strong deviation from linearity at low temperatures, i.e., non-Arrhenius behavior. This marked non-linear behavior is characteristic of a quantum mechanical tunneling event such as the translocation of hydrogen. An excellent candidate for the tunnelling process is the hydrogen of the protonated Schiff base formed between opsin and its retinal chromophore. Deuterium-exchanged rhodopsin, in which the Schiff base hydrogen is replaced by a deuterium, also shows a marked non-Arrhenius temperature dependence at low temperatures, consistent with tunneling. The rate of formation of prelumirhodopsin in deuterium-exchanged samples is much slower and a deuterium isotope effect kH/kD approximately or equal to 7 is observed. The data support a model in which the formation of prelumirhodopsin involves translocation of a proton toward the Schiff base nitrogen of the retinal chromophore.
