Tarou Ogurusu

Effects of chloride on the absorption spectrum and photoreactions of halorhodopsin

The absorption maximum of halorhodopsin in a membrane fraction prepared from the cells of Halobacterium halobium under low-salt conditions shifted to longer wavelenghts upon addition of NaCl (Ogurusu, T., Maeda, A., Sasaki, N. and Yoshizawa, T. (1981) J. Biochem. (Tokyo) 90, 1267–1273). This bathochromic shift was due to chloride, not sodium. Bromide and iodide were also effective. The bathochromic shift of the absorption maximum was not accompanied by any change in the isomer composition of retinal in halorhodopsin. The same ionic species were essential for the formation of the hypsochromic photoproduct at −75°C. These effects of NaCl on halorhodopsin are discussed in terms of the presence of the two forms of halorhodopsin, a form binding chloride and a chloride-free form.

Formation of a 7-cis retinal pigment by irradiating cattle rhodopsin at low temperatures

All the mono& isomers of retinal including the 74s can be produced by a conventional irradiation technique from all-trans retinal in a variety of polar organic solvents [ 1,2] . However, so far irradiation of cattle or frog rhodopsin at liquid nitrogen temperatures have yielded only photoproducts of rhodopsin with all-trans and 9cis retinals as their chromophores [3]. More than ten years ago, Hubbard et al. [4] suggested the possibility of the formation of isomers other than all-trans, 9cis and 11 cis retinals by irradiating rhodopsin at low temperatures. In this paper we have irradiated cattle rhodopsin in rod outer segments and analyzed the chromophoric retinals of the photoproducts using high performance liquid chromatography (HPCL), which provides a high resolving power for all the mono-cis isomers of retinals [1,2,5-71. We have found that a photoproduct binding 7cis retinal as a chromophore can be produced by irradiating rhodopsin at -75°C.