m-Fluorotyrosine substitution in β-galactosidase; Evidence for the existence of a catalytically active tyrosine

M. Ring, I. M. Armitage, R. E. Huber

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

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 languageEnglish (US)
Pages (from-to)675-680
Number of pages6
JournalBiochemical and Biophysical Research Communications
Volume131
Issue number2
DOIs
StatePublished - 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.

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