Skip to main content
PMC home page
Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1973 Jul;70(7):1986–1989. doi: 10.1073/pnas.70.7.1986

Carbon Dioxide Hydration Activity of Carbonic Anhydrase: Paradoxical Consequences of the Unusually Rapid Catalysis*

Raja G Khalifah 1,2
PMCID: PMC433648  PMID: 4198662

Abstract

The kinetic parameters for carbon dioxide hydration catalysis by carbonic anhydrase (EC 4.2.1.1) present an apparent paradox. The assumption of H2CO3 as the hydration product requires the rate of recombination of H2CO3 with enzyme to be faster than the diffusion limit. The alternative assumption of HCO3- as the product of hydration likewise requires active-site ionization rates to exceed the diffusion limit. We previously postulated the presence of special means for rapid active-site ionization. It is shown here that when proton transfer between enzyme and buffer species is taken into account, there is no need to invoke rates exceeding the diffusion limit. Bicarbonate ion thus appears as the most probable hydration product and dehydration substrate.

Keywords: enzymes, mechanism, acid-base catalysis, diffusion limit

Full text

PDF
1986

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Caplow M. Bromine catalysis for carbon dioxide hydration and dehydration and some observations concerning the mechanism of carbonic anhydrase. J Am Chem Soc. 1971 Jan 13;93(1):230–235. doi: 10.1021/ja00730a038. [DOI] [PubMed] [Google Scholar]
  2. EIGEN M., HAMMES G. G. ELEMENTARY STEPS IN ENZYME REACTIONS (AS STUDIED BY RELAXATION SPECTROMETRY). Adv Enzymol Relat Areas Mol Biol. 1963;25:1–38. doi: 10.1002/9780470122709.ch1. [DOI] [PubMed] [Google Scholar]
  3. GIBBONS B. H., EDSALL J. T. KINETIC STUDIES OF HUMAN CARBONIC ANHYDRASES B AND C. J Biol Chem. 1964 Aug;239:2539–2544. [PubMed] [Google Scholar]
  4. KERNOHAN J. C. THE PH-ACTIVITY CURVE OF BOVINE CARBONIC ANHYDRASE AND ITS RELATIONSHIP TO THE INHIBITION OF THE ENZYME BY ANIONS. Biochim Biophys Acta. 1965 Feb 22;96:304–317. [PubMed] [Google Scholar]
  5. Khalifah R. G., Edsall J. T. Carbon dioxide hydration activity of carbonic anhydrase: kinetics of alkylated anhydrases B and C from humans (metalloenzymes-isoenzymes-active sites-mechanism). Proc Natl Acad Sci U S A. 1972 Jan;69(1):172–176. doi: 10.1073/pnas.69.1.172. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Khalifah R. G. The carbon dioxide hydration activity of carbonic anhydrase. I. Stop-flow kinetic studies on the native human isoenzymes B and C. J Biol Chem. 1971 Apr 25;246(8):2561–2573. [PubMed] [Google Scholar]
  7. Koenig S. H., Brown R. D., 3rd H 2 CO 3 as substrate for carbonic anhydrase in the dehydration of HCO 3 . Proc Natl Acad Sci U S A. 1972 Sep;69(9):2422–2425. doi: 10.1073/pnas.69.9.2422. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Proceedings of the National Academy of Sciences of the United States of America are provided here courtesy of National Academy of Sciences

RESOURCES