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Kinetic Characterization of Ca 2+ Transport in Synaptic Membranes
Author(s) -
Javors M. A.,
Bowden C. L.,
Ross D. H.
Publication year - 1981
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1981.tb00466.x
Subject(s) - membrane , atpase , biophysics , chemistry , calcium , lysis , synaptosome , phosphorylation , kinetics , biochemistry , enzyme , biology , physics , organic chemistry , quantum mechanics
Lysed synaptosomal membranes were prepared from brain cortices of HA/ICR Swiss mice, and the ATP‐stimulated Ca 2+ uptake, Ca 2+ ‐stimulated Mg 2+ ‐dependent ATPase activity, and the Ca 2+ ‐stimulated acyl phosphorylation of these membranes were studied. The K m values for free calcium concentrations ([Ca 2+ ] f ) for these processes were 0.50 μM, 0.40 μM, and 0.31 μM, respectively. Two kinetically distinct binding sites for ATP were observed for the ATP‐stimulated Ca 2+ uptake and the Ca 2+ ‐stimulated Mg 2+ ‐ATPase activity. The high‐affinity K m values for ATP for these two processes were 16.3 μM, and 28 μM, respectively. These results indicate that the processes studied operate in similar physiological concentration ranges for the substrates [Ca 2+ ] f and ATP under identical assay conditions and, further, that these processes may be functionally coupled in the membrane.