Vertebrate photoreceptors

The basis of the duplex theory of vision is examined in view of the dazzlin g array of data on visual pigment sequences and the pigments they form, on the microspectrophotometry measurements of single photoreceptor cells, on t he kinds of photoreceptor cascade enzymes, and on the electrophysiological properties of photoreceptors. The implications of the existence of five dis tinct visual pigment families are explored, especially with regard to what pigments are in what types of photoreceptors, if there are different photot ransduction enzymes associated with different types of photoreceptors, and if there are electrophysiological differences between different types of co nes. (C) 2000 Elsevier Science Ltd. All rights reserved.