Histidine 64 is not required for high CO2 hydration activity of human carbonic anhydrase II
Open Access
- 14 March 1988
- journal article
- research article
- Published by Wiley in FEBS Letters
- Vol. 229 (2) , 360-362
- https://doi.org/10.1016/0014-5793(88)81156-6
Abstract
To test the hypothesis that histidine 64 in carbonic anhydrase II has a crucial role as a ‘proton shuttle group’ during catalysis of CO2-HCO− 3 interconversion, this residue was replaced by lysine, glutamine, glutamic acid and alanine by site-directed mutagenesis. All these variants turned out to have high CO2 hydration activities. The k cat values at pH 8.8 and 25°C were only reduced by 1.5–3.5-fold compared to the unmodified enzyme. These results show that intramolecular proton transfer via His 64 is not a dominating pathway in the catalytic reaction. The variants also catalyze the hydrolysis of 4-nitrophenyl acetate. The pK a values for the activity-controlling group are between 6.8 and 7.0 for all studied forms of the enzyme except the Glu 64 variant which shows a complex pH dependence with the major pK a shifted to 8.4Keywords
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