PMID: 2498877May 1, 1989Paper

An estimate of the number of G regulator proteins activated per excited rhodopsin in living Limulus ventral photoreceptors

Proceedings of the National Academy of Sciences of the United States of America
A KirkwoodJ E Lisman

Abstract

Previous work by others on Limulus photoreceptors has shown that application of a variety of guanine nucleotide-binding regulatory protein (G protein) activators produces discrete waves of depolarization similar to those generated by single photos, but smaller in size. We investigated whether these events might originate at a site other than the G protein. Initiation of the events did not depend on the state of the visual pigment, suggesting that the events do not originate at the pigment level. The events could be blocked by the G-protein blocker guanosine 5'-[beta-thio]diphosphate (GDP[betaS]) and thus support the conclusion that these discrete events are due to the activation of G protein itself. Quantitative measurements indicate that the average size of these events is approximately 8 times smaller than that evoked by single photons under the same conditions. Given certain reasonable assumptions, these results imply that the gain of the first stage of transduction in vivo is approximately 8, a value considerably lower than that measured in vitro in vertebrate rods (gain, 100-500). Furthermore, independent evidence for a low first-stage gain in Limulus is derived from the observation that GDP[betaS] barely affects the size ...Continue Reading

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Citations

Aug 1, 1996·Journal of Photochemistry and Photobiology. B, Biology·R Payne, K Ukhanov
Jul 1, 1993·Proceedings of the National Academy of Sciences of the United States of America·W C SmithB A Battelle
Apr 1, 1994·The Journal of General Physiology·A Kirkwood, J E Lisman
Jul 1, 1995·Photochemistry and Photobiology·W Gärtner, P Towner
May 12, 2000·Nature Cell Biology·B CookB Minke
Dec 23, 2004·American Journal of Physiology. Cell Physiology·Hideo AkiyamaMasahiko Kurabayashi
Oct 1, 1995·Evolution; International Journal of Organic Evolution·Adrian M PatersonRussell D Gray

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