Dc ;pnr.ter?~ent de Cl~ir?lie, Uni~vrsitP Lnvnl, Q~lPbec 10, Quebec GIK 7P4 R e~u le 15 fevrier 1974MARIUS JULIEX et L u~o v r c OUELLET. Can. J. Chem. 52, 3087 (1974). Le r6le de la charge de la niolCcule d'enzyme dans la cinetique de la reaction catalysee par diverses phosphatases alcalines a Cte etudie. Les donnees experimentales obtenues en utilisant le phosphate de p-nitrophenyle (charge nette -2 ) cornrne substrat montrent que la repulsion entre le molecule d'enzyme, de charge negative, et la molecule de substrat peut tenir compte, quantitativement, de la variation de la constante de Michaelis du systeme avec le p H entre p H 8.5 et p H 10.5. Toutefois les resultats obtenus en utilisant le phosphate d'ethanolamine (charge nette, -1) et dep-ou o-carboxyphenyle (charge nette -3) montrent soit que la partie organique de la molecule de substrat ne joue aucun r61e dans la formation du complexe enzyme-substrat, ou que la charge de la molecule d'enzyme ne joue pas le r6le suggere par les resultats obtenus avec le phosphate de p-nitrophenyle.Une etude plus pousske de cette derniere reaction en variant la force ionique et la constante dielectrique du milieu suggere que le centre actif de la molecule d'enzyme soit porteur d'une charge positive, et soit hydrophobe. MARIWS JULIEN and L U D~V I COUELLET. Can. J. Chem. 52, 3087 (1974). The role played by the ionic charge of the enzyme in the kinetics of the reactions catalyzed by alkaline phosphatases has been investigated. Data obtained from the hydrolysis ofp-nitrophenyl phosphatc (net charge -2 ) indicate that the repulsion between the negatively charged enzyme molecule and the substrate molecule is sufficient to take into account, quantitatively, the variation of the Michaelis constant with the p H o f the system between pH8.5 and 10.5. However, the results obtained with ethanolamine phosphate (net charge -I ) and p-or o-carboxyphenyl phosphate (net charge -3) show that either the organic part of the substrate molecule is not involved in the formation of the enzyme substrate intermediate or the charge of the enzyme does not have the role suggested from the work with p-nitrophenyl phosphate.Further investigation of this reaction in solutions of various ionic strength and dielectric constants suggests that the active center of the enzyme m~olecule is positively charged, but that hydrophobic effects are important. IntroductionLa phosphatase alcaline intestinale de veau (EC 3.1.3.1.)
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