Reexamination of the role of Asp20 in catalysis by bacteriophage T4 lysozyme |
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Authors: | L W Hardy A R Poteete |
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Affiliation: | Department of Molecular Genetics and Microbiology, University of Massachusetts, Worcester 01655. |
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Abstract: | Replacement of Asp20 in T4 lysozyme by Cys produces a variant with (1) nearly wild-type specific activity, (2) a newly acquired sensitivity to thiol-modifying reagents, and (3) a pH-activity profile that is very similar to that of the wild-type enzyme. These results indicate that the residue at position 20 has a significant nucleophilic function rather than merely an electrostatic role. The intermediate in catalysis by lysozyme is probably a covalent glycosyl-enzyme instead of the ion pair originally proposed. |
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