Kinetic Characterization of Ca2+ Transport in Synaptic Membranes |
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| Authors: | M. A. Javors,C. L. Bowden,D. H. Ross&dagger |
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| Affiliation: | Department of Psychiatry, The University of Texas Health Science Center, Sun Antonio, Texas, U.S.A.;Department of Pharmacology, The University of Texas Health Science Center, Sun Antonio, Texas, U.S.A. |
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| Abstract: | Lysed synaptosomal membranes were prepared from brain cortices of HA/ICR Swiss mice, and the ATP-stimulated Ca2+ uptake, Ca2+-stimulated Mg2+-dependent ATPase activity, and the Ca2+-stimulated acyl phosphorylation of these membranes were studied. The Km values for free calcium concentrations ([Ca2+]f) for these processes were 0.50 microM, 0.40 microM, and 0.31 microM, respectively. Two kinetically distinct binding sites for ATP were observed for the ATP-stimulated Ca2+ uptake and the Ca2+-stimulated Mg2+-ATPase activity. The high-affinity Km values for ATP for these two processes were 16.3 microM and 28 microM, respectively. These results indicate that the processes studied operate in similar physiological concentration ranges for the substrates [Ca2+]f and ATP under identical assay conditions and, further, that these processes may be functionally coupled in the membrane. |
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| Keywords: | Ca2+-Mg2+-ATPase activity ATP-dependent Ca2+ uptake Ca2+ transport protein Ca2+-stimulated acyl phosphorylation Cation transport |
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