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Solvent Deuterium Isotope Effect on the Binding of β-d-Galactopyranosyl Derivatives to β-Galactosidase (Escherichia coli, lac Z)

✍ Scribed by John P. Richard; Deborah A. McCall

Publisher: Elsevier Science
Year: 2000
Tongue: English
Weight: 68 KB
Volume: 28
Category: Article
ISSN: 0045-2068
DOI: 10.1006/bioo.1999.1157

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✦ Synopsis

A value of 1.8 has been determined for (K I ) HOH /(K I ) DOD , the ratio of the values of K I for competitive inhibition of β-galactosidase by isopropyl β-D-thiogalactopyranoside in H 2 O and D 2 O. This is similar to the value of 1.7 for (K m ) HOH /(K m ) DOD , the ratio of the Michaelis constants determined for the β-galactosidase-catalyzed hydrolysis of 4-nitrophenyl β-Dgalactopyranoside (Gal-OPNP) in H 2 O and D 2 O. The similarity of these solvent deuterium isotope effects suggests that the observed isotope effect on K m corresponds, mainly, to the isotope effect on the dissociation constant K d for Gal-OPNP. The implications of these results for the interpretation of the solvent deuterium isotope effects on k cat and k cat /K m for β-galactosidase-catalyzed hydrolysis of Gal-OPNP is discussed.

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Effect of an E461G Mutation of β-Galactosidase (Escherichia coli, lac Z) on pL Rate Profiles and Solvent Deuterium Isotope Effects

✍ John P. Richard; Reuben E. Huber; Deborah A. McCall 📂 Article 📅 2001 🏛 Elsevier Science 🌐 English ⚖ 116 KB

An E461G mutation of ␤-galactosidase results in the disappearance of the high pL (L ϭ H, D) downward break in the rate profiles for k cat /K m for wild-type enzyme-catalyzed hydrolysis of 4-nitrophenyl ␤-D-galactopyranoside (Gal-OPNP) and a decrease from (k cat ) HOH /(k cat ) DOD ϭ 1.7 to (k cat )