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PMID:3126084
| Citation |
Forsman, C, Behravan, G, Jonsson, BH, Liang, ZW, Lindskog, S, Ren, XL, Sandström, J and Wallgren, K (1988) Histidine 64 is not required for high CO2 hydration activity of human carbonic anhydrase II. FEBS Lett. 229:360-2 |
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| 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-HCO3- 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 kcat values at pH 8.8 and 25 degrees 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 pKa 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 pKa shifted to 8.4. |
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| Keywords |
Binding Sites; Carbon Dioxide/metabolism; Carbonic Anhydrases/genetics; Carbonic Anhydrases/metabolism; DNA/genetics; Escherichia coli/enzymology; Fetus; Histidine; Humans; Kinetics; Liver/enzymology; Protein Binding |
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Significance
Annotations
| Gene product | Qualifier | GO Term | Evidence Code | with/from | Aspect | Extension | Notes | Status |
|---|---|---|---|---|---|---|---|---|
| GO:0004064: arylesterase activity |
ECO:0000315: |
F |
Table 2 shows the effect of mutations at residue 64 on kinetic constants for hydrolysis of 4-nitrophenyl acetate by purified human CAHII. Because this reaction is the hydrolysis of a phenyl acetate, this protein has arylesterase activity. |
complete | ||||
|
enables |
GO:0004064: arylesterase activity |
ECO:0000315: mutant phenotype evidence used in manual assertion |
F |
Seeded From UniProt |
complete | |||
See also
References
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