Intramolecular and intermolecular enzymatic modulation of ion channels in excised membrane patches

Biophysical Journal
K Bielefeldt, M B Jackson

Abstract

A calcium-activated potassium channel in posterior pituitary nerve terminals was modulated by phosphorylation and dephosphorylation. Nearly every patch of membrane containing this channel also contained both membrane bound protein phosphatase and membrane-bound protein kinase. By examining the statistical and kinetic nature of phosphorylation and dephosphorylation in excised patches, it was possible to evaluate two contrasting models for these enzymatic reactions. One of these models treated catalysis as an intermolecular process in which the enzyme and substrate are separate molecular species that diffuse and encounter one another during collisions. The second model treated catalysis as an intramolecular process in which the enzyme and substrate reside within a stable macromolecular complex. The study began with a Poisson analysis of the distribution of channel number in patches, and of the number of protein phosphatase-free and protein kinase-free patches. Subsequent kinetic analysis of dephosphorylation yielded an estimate of the mean number of protein phosphatase molecules per patch that was similar to the value obtained from Poisson analysis. Because these two estimates were independent predictions based on the intermolecu...Continue Reading

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Jul 10, 2004·Pflügers Archiv : European journal of physiology·Craig B NeylonPeter H Reinhart
May 6, 1996·Biochimica Et Biophysica Acta·F Becq
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Jul 3, 1999·Physiological Reviews·A MeirR Rahamimoff
Aug 18, 2001·Science·I B Levitan, S M Cibulsky

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