ISSN:
1573-6881
Keywords:
Ca2+-ATPase
;
internal calcium regulation
;
ionophore A23187
;
sarcoplasmic reticulum vesicles
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Physics
Notes:
Abstract The dependence of the Ca2+-ATPase activity of sarcoplasmic reticulum vesicles upon the intravesicular concentration of calcium accumulated after active uptake was studied. The internal calcium concentration was modified by addition of the ionophore A23187 at the steady state of accumulation. About half of the calcium accumulated could be released at low ionophore concentration without any concomitant activation of the Ca2+-ATPase. This population of calcium might consist of calcium free in the lumen of the vesicles or bound to the bilayer at sites which do not interact with the ATPase activity. At higher concentrations of ionophore (above 1.75 nmol A23187/mg protein) the release of calcium activated this enzyme. This phenomenon was independent of the extravesicular calcium concentration and might be explained by assuming second species of calcium ions bound to the inner side of the membrane and in close functional interaction with the Ca2+-ATPase.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00770033
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