THE PHOTOREACTIONS AND PHOTOSENSITIVITY OF 3,4-DEHYDRO-BACTERIORHODOPSIN AT LOW TEMPERATURES

Abstract— The photoreaction of the artificial pigment synthesized from bacterioopsin and rrans-3,4-dehydro-retinal, 3,4-dehydro]bacteriorhodopsin (3,4-deH]bR^t) was investigated with low temperature spectrophotometry.
The amount of batho-product formed from the light-adapted pigment of 3,4-deH]bR (designated as batho-3,4-deH]bR^t) by irradiation at 77 K was much less than that from trans -bacteriorhodopsin (bR^t) and depends on temperature at irradiation of the sample. The kinetics of photoconversion of 3,4-deH]bR^t to batho-3,4-deH]bR^t and that of its reversion were measured at several temperatures with a so-called "double Dewar system". The results showed that the photosensitivity of 3,4-deH]bR^t was temperature dependent. When batho-3,4-deH]bR^t was warmed above 143 K, it was converted to lumi-3,4-deH]bR^t. Lumi-3,4-deH]bR^t was also produced by irradiation of 3,4-deH]bR^t at 143 or 163 K. The maximum in the difference spectrum between lumi-3,4-deH]bR^t and 3,4-deH]bR^t was located at about 540 nm. The irradiation of 3,4-deH]bR^t at 183 K produced an intermediate analogous to meta-bR^t, but under similar conditions bR^t does not produce meta-bR^t. These results indicate that intermediates of 3,4-deH]bR^t are less stable than those of bR^t.
The differences between bacteriorhodopsin and 3,4-dehydro]bacteriorhodopsin were discussed and compared with the differences between rhodopsin and 3,4-dehydro]rhodopsin.