ISSN:
1432-1424
Keywords:
cryptand
;
Na+ selectivity
;
temperature
;
ionizable mobile carrier
;
nonactin
;
cation transport kinetics
;
lipid membrane
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The kinetics of Na+ and K+ transport across the membrane of large unilamellar vesicles (LUV) were determined at two pH's when transport was induced by (221)C10-cryptand (diaza-1,10-decyl-5-pentaoxa-4,7,13,16,21-bicyclo [8.8.5.] tricosane) at various temperatures, and by nonactin at 25°C and (222)C10-cryptand at 20 and 25°C. The rate of Na+ and K+ transport by (221)C10 saturated with the cation and carrier concentrations. Transport was noncooperative and exhibited selectivity for Na+ with respect to K+. The apparent affinity of (221)C10 for Na+ was higher and less pH-dependent than that for K+, and seven times higher than that of (222)C10 for K+ ions (20.5vs. 1.7 kcal·mole−). The efficiency of (221)C10 transport of Na+ was pH-and carrier concentration-dependent, and was similar to that of nonactin; its activation energy was similar to that for (222)C10 transport of K+ (35.5 and 29.7 kcal · mole−1, respectively). The reaction orders in cationn(S) and in carrierm(M), respectively, increased and decreased as the temperature rose, and were both independent of carrier or cation concentrations; in most cases they varied slightly with the pH.n(S) varied with the cation at pH 8.7 and with the carrier for Na+ transport only, whilem(M) always depended on the type of cation and carrier. Results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01869415
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