Mathematical modelling of ATP, K and Na interactions with (Na + K)-ATPase occurring under equilibrium conditions |
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Authors: | Richard Grosse, Tom Rapoport, Johannes Malur, J rg Fischer, Kurt R.H. Repke,Ian M. Glynn |
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Affiliation: | Richard Grosse, Tom Rapoport, Johannes Malur, Jörg Fischer, Kurt R.H. Repke,Ian M. Glynn |
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Abstract: | The controlling effect of ATP, K+ and Na+ on the rate of (Na+ + K+)-ATPase inactivation by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) is used for the mathematical modelling of the interaction of the effectors with the enzyme under equilibrium conditions. 1. 1. Of a series of conceivable interaction models, designed without conceptual restrictions to describe the effector control of inactivation kinetics, only one fits the experimental data described in a preceding paper. 2. 2. The model is characterized by the coexistence of two binding sites for ATP and the coexistence of two separate binding sites for K+ and Na+ on the enzyme-ATP complex. On the basis of this model, the effector parameters fitting the experimental data most closely are estimated by means of nonlinear least-squares fits. 3. 3. The apparent dissociation constants for ATP of the enzyme-ATP complex or of the enzyme-(ATP)2 complex are computed to lie near 0.0024 mM and 0.34 mM, respectively, irrespective of whether K+ and Na+ were absent or K+ and K+ plus Na+, respectively, were present in the experiments. 4. 4. The origin of the high and the low affinity site for binding of ATP to the (Na+ + K+)-ATPase molecule is traced back to the coexistence of two catalytic centres which, although primarily equivalent as to the reactivity of their thiol groups with NBD-Cl, are induced into anticooperative communication by ATP binding and thus show an induced geometric asymmetry. Keywords: (Na+ + K+)-ATPase; SH-group alkylation; Inactivation kinetics; Mathematical modelling; Substrate affinity |
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Keywords: | (Na+ + K+)-ATPase SH-group alkylation Inactivation kinetics Mathematical modelling Substrate affinity |
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