Proton transfer to residues of basic pK(a) during catalysis by carbonic anhydrase
| Autor: | J Nicole Earnhardt, Nina R. Wadhwa, Minzhang Qian, Philip J. Laipis, David N. Silverman, Chingkuang Tu |
|---|---|
| Rok vydání: | 1999 |
| Předmět: |
Stereochemistry
Carbonic anhydrase II Inorganic chemistry Biophysics chemistry.chemical_element Zinc Buffers Biochemistry Catalysis Structural Biology Carbonic anhydrase Animals Humans Molecular Biology Histidine Carbonic Anhydrases chemistry.chemical_classification biology Carbon Dioxide Hydrogen-Ion Concentration Acceptor Isoenzymes Solutions Kinetics Enzyme chemistry Intramolecular force biology.protein Protons |
| Zdroj: | Biochimica et biophysica acta. 1434(1) |
| ISSN: | 0006-3002 |
| Popis: | The maximal velocity in the hydration of CO 2 catalyzed by the carbonic anhydrases in well-buffered solutions is limited by an intramolecular proton transfer from zinc-bound water to acceptor groups of the enzyme and hence to buffer in solution. Stopped-flow spectrophotometry was used to accumulate evidence that this maximal velocity is affected by residues of basic p K a , near 8 to above 9, in catalysis of the hydration of CO 2 by carbonic anhydrases III, IV, V, and VII. A mutant of carbonic anhydrase II containing the replacement His-64→Ala, which removes the prominent histidine proton shuttle (with p K a near 7), allows better observation of these basic groups. We suggest this feature of catalysis is general for the human and animal carbonic anhydrases and is due to residues of basic p K a , predominantly lysines and tyrosines more distant from the zinc than His-64, that act as proton acceptors. These groups supplement the well-studied proton transfer from zinc-bound water to His-64 in the most efficient of the carbonic anhydrases, isozymes II, IV, and VII. |
| Databáze: | OpenAIRE |
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