A model for the recovery kinetics of rod phototransduction, based on the enzymatic deactivation of rhodopsin

Biophysical Journal
U Laitko, K P Hofmann

Abstract

We propose a model for the recovery of the retinal rod photoresponse after a short stimulus. The approach describes the enzymatic deactivation of the photoactivated receptor, rhodopsin, by simple enzyme kinetics. An important feature of this description is that the R* deactivation obeys different time laws, depending on the numbers of R* formed per disc membrane and available enzyme molecules. If the enzyme works below substrate saturation, the rate of deactivation depends linearly on the number of R*, whereas for substrate saturation a hyperbolic relation--the well-known Michaelis-Menten equation--applies. This dichotomy is used to explain experimental finding that the relation between the saturation time of the photoresponse after short illumination and the flash strength has two sharply separated branches for low and high flash intensities (up to approximately 10% bleaching). By relating both branches to properties of the enzymatic rhodopsin deactivation, the new model transcends the classical notion of a constant characteristic lifetime of activated rhodopsin. With parameters that are plausible in the light of the available data and the additional information that the deactivating enzyme, rhodopsin kinase, and the signaling...Continue Reading

References

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Citations

Jun 8, 2001·Progress in Retinal and Eye Research·J K McBeeD R Pepperberg
May 13, 1999·Proceedings of the National Academy of Sciences of the United States of America·F DickerM J Lohse
Jun 9, 2005·Experimental Eye Research·Young Hee KimGyeong Jae Cho
Jan 8, 2017·Vision Research·Ezequiel M SalidoClaudio Verrastro
Sep 17, 2009·Molecular BioSystems·Daniele Dell'OrcoFrancesca Fanelli
Oct 13, 2005·The Journal of Biological Chemistry·Guang W ShiJeannie Chen
Mar 19, 2008·The Journal of Physical Chemistry. B·Daniele Dell'Orco, Henning Schmidt

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