The kinetics of Na+ activation of brush border sucrase (sucrose D-glucosidase E.C. 3.2.1.48) has been studied in mice intestine. At pH 5.0, 50 mM Na+ ions stimulated sucrase activity by 84%. At pH 7.2, enzyme stimulation was reduced to 16%, whereas, atpH 8.5, 10-100 mMNa+ ions produced 18-45% inhibition of enzyme activity. Kinetic studies revealed that at pH 5.0, the enzyme activation by Na+ ions was V-type, which changed to K-type atpH 7.2, whereas at alkaline pH (8.5), Na+ ions inhibited the enzyme activity non-competitively. Using the non-compulsory model of Na+ ion stimulation of brush border sucrase [Mahmood & Alvarado, Arch Bioch Biophys, 168 (1975) 585] various kinetic constants involved in activation of sucrase by Na ions were determined. It is apparent that Na+ stimulation of brush border sucrase is pH dependent, which is similar to that described for rat, rabbit and other mammalian species and conform to identical mechanisms, at least with reference to the affinity type effects, as observed in mice intestine.
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