The sulfhydryl group microenvironment of lactose synthase from bovine milk |
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Authors: | L J Wong S S Wong |
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Affiliation: | 1. The Biochemistry Program, Departments of Biological Sciences, University of Lowell. Lowell, MA 01854, U.S.A. [Tel. 617-425-5000];2. The Biochemistry Program, Departments of chemistry, University of Lowell. Lowell, MA 01854, U.S.A. [Tel. 617-425-5000] |
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Abstract: | Galactosyltransferase from bovine milk was inactivated by a series of sulfhydryl group specific reagents of different structures and sizes. The inactivation rate constants suggest that the thiol is located in a nonpolar microenvironment. The ESR spectrum of a spin labeled galactosyltransferase showed that the sulfhydryl group is in a region of non-restricted rotation, consistent with its broad reactivity towards various thiol reagents. Galactosyltransferase immobilized onto agarose through its sulfhydryl group retained its ability to catalyze the synthesis of N-acetyllactosamine and lactose. Thus the residual activity of the sulfhydryl group modified enzyme is not due to an isozyme lacking such a group. In addition, the active thiol can not be located at the active site nor the protein-protein interaction site between galactosyltransferase and alpha-lactalbumin. |
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