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Two mechanisms of nonactin mediated K<sup>+</sup> ion transport across phospholipid vesicular membranes

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Title Two mechanisms of nonactin mediated K+ ion transport across phospholipid vesicular membranes
 
Creator Prabhananda, B S
Kombrabail, Mamata H
 
Description 283-293
From kinetic data it has been possible to
show that when a weak acid such as carbonyl cyanide m-chlorophenylhydrazone
(CCCP) is also present in phospholipid vesicles the ionophore nonactin (NON) transports
K+ ions across the membrane by two mechanisms: (I) As the charged species
NON-K+ and (II) as the electroneutral complex NON-K+- CCCP-.
In mechanism I, the anion CCCP- is also translocated across the membrane
as charged species such that the net charge translocated is zero. In the earlier
experiments using valinomycin (VAL) and CCCP (Prabhananda B S & Kombrabail M
H (1995) Biochim, Biophys, Acta 1235, 323-335) the existence
of a mechanism similar to mechanism I could not be detected. Even with NON (instead
of VAL), at the concentrations of our experiments mechanism II is dominant. The
relative dominance of mechanism II could be decreased either (i), by lowering the
ionophore concentration or (ii), by "catalysing" the transport of
CCCP- from the "polar region" to the "nonpolar region"
of the membrane by adding VAL at small concentrations. The kinetics of K+
transport used in arriving at such conclusions were inferred from the rate of decay
of H+ concentration difference (ΔpH) across phospholipid vesicular
membrane after creating ΔpH by temperature jump. A new procedure has been
used to estimate the translocation rate constant k+ of NON-K+
in soybean phospholipid vesicles (~1.5 × 103 s-1) by identifying
the NON-K+ translocation limited contribution to 1/τ by the combined
action of NON, CCCP and tetraphenylphosphonium ions (TPP+). The apparent
K+ dissociation constant of NON-K+ (~ 0.14 M), dissociation
constant of NON-K+- CCCP - in the membrane (~30mM),
and translocation rate constant of NON-K+- CCCP - (k0~
4.2×103 s-1) have been determined in soybean phospholipid
vesicle solutions containing 100 mM KCl.
 
Date 2013-07-16T08:57:43Z
2013-07-16T08:57:43Z
2000-10
 
Type Article
 
Identifier 0975-0959 (Online); 0301-1208 (Print)
http://hdl.handle.net/123456789/19834
 
Language en_US
 
Rights CC Attribution-Noncommercial-No Derivative Works 2.5 India
 
Publisher NISCAIR-CSIR, India
 
Source IJBB Vol.37(5) [October 2000]