Transducin and the Cyclic GMP Phosphodiesterase: Amplifier Proteins in Vision
This extract was created in the absence of an abstract.
Excerpt
Retinal rod cells display two striking properties. First, they are exquisitely sensitive detectors. Psychophysical and electrophysiological studies have shown that rod cells can be excited by a single photon. Second, their sensitivity is regulated, enabling them to perceive contrast over a millionfold range of the background light level. The molecular machinery for excitation and adaptation is localized in a discrete portion of the cell, the outer segment, which can readily be detached and harvested in large quantity. Rod outer segments (ROS) are gifts of nature for the study of molecular mechanisms of amplification and gain control by sensory systems.
Excitation is triggered by the photoisomerization of the 11-cis retinal chromophore of rhodopsin to the all-trans form. This conformational transition in a single photoreceptor protein molecule leads to the transient closure of many Na+ channels in the plasma membrane of the outer segment (for reviews, see Hubbell and Bownds 1979; Matthews...
