Thermal Recovery of Iodopsin from Photobleaching Intermediates^†

Abstract

The chloride effect on the photobleaching process of iodopsin, a chicken red-sensitive cone visual pigment, was studied in detail by time-resolved low-temperature spectroscopy at -40 degrees C to -10 degrees C. Decay-associated difference spectra obtained by kinetic analysis using the singular value decomposition method were composed of spectra of BL-iodopsin, lumiiodopsin, metaiodopsin I, metaiodopsin II and metaiodopsin III, essentially identical to those at room temperature. In each conversion step however, iodopsin was partially regenerated, which is not observed in the bleaching process for other visual pigments or iodopsin at room temperature. Moreover, iodopsin was slowly regenerated from the bleached species. The reverse reactions were completely suppressed by substitution of lyotropic NO(3)(-) for Cl(-), suggesting that Cl(-) binding to iodopsin interferes with light-induced cis-trans isomerization of the chromophore. It is likely that the water molecule hydrating Cl(-) forms the additional hydrogen bond(s), by which the protein conformational change necessary to release this steric hindrance becomes enthalpic. As progress of the bleaching process is a consequence of protein conformational change, it is suppressed at low temperatures, resulting in thermal back-isomerization.

Rapid Oxidation Following Photoreduction in the Avian Cryptochrome4 Photocycle

“…Spectral data were analyzed using SVD analysis, as well as Global Fitting in Igor Pro 6.22J (WaveMetrics), according to previously described methods. − …”

Red-Tuning of the Channelrhodopsin Spectrum Using Long Conjugated Retinal Analogues

“…For the time-resolved analyses of photocycles, the spectral changes were analyzed by the singular-value decomposition (SVD) method, which was described in our previous study in detail. 43,44 In short, the data sets of transient difference spectra were arranged in a matrix A, in which the columns and rows correspond to wavelength and time after photoexcitation, respectively. The SVD calculation decomposed A into the product of a left singular matrix U, a diagonal matrix containing singular values S, and a transpose of a right singular matrix V. If the difference in amplitudes between the ith and (i +1)th singular values was significantly greater than that between the (i+1)th and (i+2)th ones, the number of significant components (n) was determined to be i as follows.…”

“…-22 -When ATR1-C1C2 was excited by a yellow flash, the absorbance decreased at 470 nm and increased at 350 nm and 530 nm as observed right after flash (Figures 3a and S1a). Then, absorbance at 350 nm decreased with concomitant increase at 530 nm, followed by absorbance decrease at 530 nm, while small loss of absorbance at 450 nm was long-lived in the photocycle.To further anatomize the spectral changes in our measurements, the series of transient difference spectra (Figure S1a) were analyzed by singular value decomposition (SVD) analysis,43,44 giving four significant U-and V-spectra.By global fitting of four V-spectra with three-exponential function, three decay associated difference spectra (B1, B2, and B3) plus constant component (B0) were calculated (Eq. 4) (Figure 4a).…”

Helical rearrangement of photoactivated rhodopsin in monomeric and dimeric forms probed by high-angle X-ray scattering

“…23 Rhodopsin in the sample was photoactivated by a yellow flash generated by a short-arc xenon flash lamp (SA200, Nissin Electronic) and a glass optical filter (Y52, Asahi Techno Glass). The transient spectra were recorded every 100 µs, and analyzed by the singular value decomposition method 21,24 executed on Igor Pro 6.3 (WaveMetrix).…”