The activation of intestinal brush border sucrase by alkali metal ions: an allosteric mechanism similar to that for the Na+-activation of nonelectrolyte transport systems in intestine. |
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Authors: | A Mahmood F Alvarado |
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Affiliation: | Department of Physiology and Biophysics, School of Medicine, University of Puerto Rico, San Juan, Puerto Rico 00936 USA |
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Abstract: | Activation of intestinal brush border sucrase by alkali-metal ions is described by an allosteric, noncompulsory mechanism involving two distinct sites: one for sucrose and another for the metal activator. Both Na+ and K+ activate guinea pig sucrase but K+ has ten times more affinity for the metal site. Li+ is inert. Values for the dissociation constants for the interaction of sucrase with either sucrose, Na+ or K+ have been calculated for the guinea pig, rat, and hamster. Qualitatively, the activation of sucrase by alkali metal ions is similar to that described for the Na+-activation of amino acid and sugar transport in intestine. However, the Na-binding site in the two systems is apparently quite different. In the guinea pig, the Na-dissociation constant is in the order of 10?3m for sucrase, about two orders of magnitude smaller than that for transport. Also, K + is a strong activator of guinea pig sucrase, but an inhibitor of intestinal sugar transport. |
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