Non-Retinal Chromophoric Proteins

Although they are not related, photoactive yellow protein (PYP), green fluorescent protein (GFP), and phytochromes are all discussed in this chapter that deals with the cis-trans isomerization (CTI) of non-retinal binding proteins. All three systems contain a chromophore that is attached to the protein and that undergoes CTI. In this chapter we attempt to provide the reader with a brief introduction to PYP, GFP, and phytochromes, and present a summary of the current understanding of the CTIs that are central to the photochemistry observed in these systems. 

The evidence to-date shows that vertebrate photoreception is mediated by a closely related group of proteins termed opsins. These are G protein-coupled receptors characterized by their ability to bind a vitamin A based chromophore ( -cis-retinal) via a Schiff base linkage using a lysine residue in the 7th transmembrane a helix (Fig. 1). The primary events of image detection by the rods and cones occurs with the absorption of a photon of light by ll-r/r-retinal and its photoisomerization to the AUtrans state (Bums Baylor 2001, Menon et al 2001). Although photoreception is best understood in retinal rods and cones, photoreception is not confined to these structures. In non-mammalian... 

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