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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
 

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m-Fluorotyrosine substitution in beta-galactosidase; evidence for the existence of a catalytically active tyrosine.

The pH profiles of beta-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 beta-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.[1]

References

  1. m-Fluorotyrosine substitution in beta-galactosidase; evidence for the existence of a catalytically active tyrosine. Ring, M., Armitage, I.M., Huber, R.E. Biochem. Biophys. Res. Commun. (1985) [Pubmed]
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