The Electronic Spectroscopy of Photoreceptors (Other Than Rhodopsin)

Sensory Perception and Transduction in Aneural Organisms

“…The above spectral "selection rules" for linear and cyclic conjugated chromophores, respectively, can be explained with the aid of "four-orbital" models in which butadiene serves as a model for all linear polyenes and benzene as a model for all cyclic polyenes (for review, see Song, 1983a). These models are schematically shown in Scheme 2.…”

“…Hund's rule) also put the ~q = ± 1 transitions at a shorter wavelength region than the ~q = ± 9 transitions. For a thorough review of this' topic, the reader is referred to a review by the lecturer (Song, 1977(Song, , 1983a.…”

“…Similar descriptions can be extended to the absorption spectra of other photoreceptor chromophores such as tryptophan, flavins, chlorophylls and retinals (see Song, 1977Song, , 1983a, for reviews).…”

“…As an example of the utility of the above observation, phytochrome (both Pr and Pfr forms) with an open-tetrapyrrole chromophore has been analyzed on the basis of dependence of the absorption spectral shape upon tetrapyrrole conformations (Song et al, 1979;Song, 1983aSong, , 1984a. The observed absorption spectra of phytochrome are, thus, best described by a semi-circular conformation of the chromophore, as shown in Fig.…”