Gain and kinetics of activation in the G-protein cascade of phototransduction

T. D. Lamb*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

80 Citations (Scopus)

Abstract

The guanine nucleotide binding protein (G protein) cascade underlying phototransduction is one of the best understood of all signaling pathways. The diffusional interactions of the proteins underlying the cascade have been analyzed, both at a macroscopic level and also in terms of the stochastic nature of the molecular contacts. In response to a single activated rhodopsin (R*) formed as a result of a single photon hit, it can be shown that molecules of the G-protein transducin will be activated approximately linearly with time. This, in turn, will cause the number of activated molecules of the effector protein (the phosphodiesterase) also to increase linearly with time. These kinetics of protein activation provide an accurate description of the time course of the rising phase of the photoreceptor's electrical response over a wide range of flash intensities. Recent estimates indicate that at room temperature each R* triggers activation of the phosphodiesterase at a rate of 1000-2000 subunits · s-1. Now that a quantitative description of the activation steps in transduction has been obtained, perhaps the greatest challenge for the future is to provide a comprehensive description of the shutoff reactions, so that a complete account of the photoreceptor's response to light can be achieved.

Original languageEnglish
Pages (from-to)566-570
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume93
Issue number2
DOIs
Publication statusPublished - 23 Jan 1996
Externally publishedYes

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