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. 1973 Sep;70(9):2505–2508. doi: 10.1073/pnas.70.9.2505

The Catalytic Mechanism of Carbonic Anhydrase

Sven Lindskog *, Joseph E Coleman †
PMCID: PMC427044  PMID: 4200327

Abstract

It is shown that an “inverse” relationship between the pH dependencies of the rates of hydration of CO2 and dehydration of HCO3- by carbonic anhydrase (EC 4.2.1.1) is a direct consequence of the thermodynamic equilibrium between CO2 and HCO3- and independent of any assumptions about the catalytic mechanism. It is further shown that proposed mechanisms for carbonic anhydrase involving HCO3- as the substrate in the dehydration reaction and a proton transfer reaction, EH+ ⇌ E + H+, as an obligatory step during catalysis obey the rule of microscopic reversibility. This includes mechanisms in which the proton dissociation is from a zinc-coordinated water molecule. Such mechanisms can be in accord with the observed rapid turnover rates of the enzyme, since rapid proton exchange can occur with the buffer components, EH+ + B ⇌ E + BH+. Mechanisms in which H2CO3 is the substrate in dehydration avoid the proton-transfer step, but require that H2CO3 combines with enzyme more rapidly than in a diffusion-controlled reaction. Physico-chemical evidence for and against a zinc-hydroxide mechanism is discussed.

Keywords: metalloenzymes, enzyme mechanism, hydration of CO2

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Selected References

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

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