EFFECT OF LIGANDS ON ROTATIONAL MOBILITY OF NA+,K+-ATPASEстатья
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Дата последнего поиска статьи во внешних источниках: 27 мая 2015 г.
Местоположение издательства:Road Town, United Kingdom
Первая страница:889
Последняя страница:894
Аннотация:The phosphorescence anisotropy of eosin-5'-isothiocyanate-labeled duck salt gland Na+,K+-ATPase was measured. The initial anisotropy was 0.235 +/- 0.015 at room temperature and did not depend on the conformation of the enzyme (sodium or potassium). The phosphorescence anisotropy decay curve was well fitted with two exponentials plus a residual term, the fast component being presumed to describe the mobility of functional units of the enzyme (protomers) and the slow component that of oligomers. In the presence of ligands modifying the conformational state of Na+,K+-ATPase (sodium, potassium, ATP), the fast component of the experimental curve was not changed, whereas the slow component changed substantially. Comparison of the rotational mobility of the labeled enzyme in the presence of ligands inducing different stages of the hydrolytic cycle suggests that interprotomer interactions are changed during ATP hydrolysis: the share of large associates is enhanced when potassium interacts with the enzyme, while the mobility of oligomers is strongly increased after ATP binding. After addition of 2% nonionic detergent C(12)E(9), the initial phosphorescence anisotropy is decreased to 0.1 and the residual term disappears while the curve remains biexponential. The difference between the rotational correlation time for the enzyme measured in the presence of sodium or potassium is decreased. The difference in the protomer/oligomer ratio between potassium or sodium containing medium becomes insignificant. This means that in the presence of detergent high molecular weight aggregates of the enzyme are solubilized, the mobility of both protomeric and oligomeric forms of the ATPase is increased, and the difference in mobility between sodium and potassium conformers disappears.