pH-dependent inhibitory effects of tris and lithium ion on intestinal brush-border sucrase

Journal of Enzyme Inhibition
M VasseurF Alvarado

Abstract

Tris and two of its hydroxylated amine analogs were examined in a metal-free, universal n-butylamine buffer, for their interaction with intestinal brush border sucrase. Our recent three-proton-families model (Vasseur, van Melle, Frangne and Alvarado (1988) Biochem. J., 251, 667-675) has provided the sucrase pK values necessary to interpret the present work. At pH 5.2, 2-amino-2-methyl-l-propanol (PM) causes activation whereas Tris has a concentration-dependent biphasic effect, first causing activation, then fully competitive inhibition. The amine species causing activation is the protonated, cationic form. The difference between the two amines is related to the fact that Tris has a much lower pKa value than PM (respectively, 8.2 and 9.8). Even at pH 5.2, Tris (but not PM) exists as a significant proportion of the free base which, by inhibiting the enzyme fully competitively, overshadows the activating effect of the cationic, protonated amine. Above pH 6.8, both Tris and PM act as fully competitive inhibitors. These inhibitions increase monotonically between pH 6.5 and 8.0 but, above pH 8, inhibition by 2.5 mM Tris tends to diminish whereas inhibition by 40 mM PM increases abruptly to be essentially complete at pH 9.3 and above....Continue Reading

References

Aug 11, 1977·Biochimica Et Biophysica Acta·A Mahmood, F Alvarado
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Citations

Feb 24, 2001·Critical Reviews in Biotechnology·R K SharmaR M Kothari
May 12, 2005·Journal of Biosciences·Jaspreet KaurSafrun Mahmood
Aug 18, 2006·Cellular Physiology and Biochemistry : International Journal of Experimental Cellular Physiology, Biochemistry, and Pharmacology·Mathie LorrotMonique Vasseur
Apr 11, 2009·Bioscience Reports·Shiffalli GuptaAkhtar Mahmood
Oct 28, 2019·Biochemistry and Biophysics Reports·Shabeer A RatherAkhtar Mahmood

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