Abstract
The pH profiles of β-galactosidase, having tyr replaced by m-fluorotyrosine, were compared to those of normal enzyme. The inflection point on the alkaline side was lowered about 1.5 pH units in the fluoro-enzyme, corresponding to the difference in the phenolic pKa values of m-fluorotyrosine and tyr. When glycosidic bond breakage was rate-limiting, the Vm at pH 7.0 was higher for the fluoro-enzyme. When hydrolysis was rate-limiting or when acceptors which made transgalactosylis rate-limiting were used, the Vm was lower for the fluoro-enzyme. This shows that a tyr in β-galactosidase is a general-acid catalyst in the glycosidic bond breaking reaction and a tyr (probably the same one) is a general-base catalyst in the hydrolytic reaction.
Original language | English (US) |
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Pages (from-to) | 675-680 |
Number of pages | 6 |
Journal | Biochemical and Biophysical Research Communications |
Volume | 131 |
Issue number | 2 |
DOIs | |
State | Published - Sep 16 1985 |
Bibliographical note
Funding Information:This work was supported by the National Council (Canada) and the Alberta Heritage
Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.