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Kinetics and Mechanism of Carbonic Anhydrase Isoenzymes a
Author(s) -
LINDSKOG SVEN,
ENGBERG PAUL,
FORSMAN CECILIA,
IBRAHIM SIRAG A.,
JONSSON BENGTHARALD,
SIMONSSON INGVAR,
TIBELL LENA
Publication year - 1984
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1984.tb12315.x
Subject(s) - chemistry , histidine , intramolecular force , carbonic anhydrase , active site , stereochemistry , molecule , titratable acid , metal , carbonic anhydrase ii , nucleophile , reaction mechanism , catalysis , enzyme , organic chemistry , biochemistry
A mechanism model has been presented that can describe most known kinetic properties of carbonic anhydrase isoenzymes I, II, and III. The essential features of this model include: Nucleophilic attack of metal-bound OH- on CO2 to form metal-bound HCO-3. Formation of metal-bound OH- from metal-bound H2O. In isoenzyme II, and probably also in isoenzyme I, this reaction step involves an intramolecular transfer of H+ between the metal site and a titratable histidine residue via a number of hydrogen-bonded H2O molecules. In isoenzyme II, this step limits the maximal rate of catalysis. Also in isoenzyme III, the H2O-splitting step may be rate limiting, but since this isoenzyme has no titratable active-site histidine, H+ transfer may take place directly with components of the solvent. In isoenzymes I and II, rapid H+ transfer between active site and solution proceeds in a reaction between the titratable histidine residue and buffer molecules. The model can also rationalize a variety of observed inhibition patterns.