The Protein Journal

, Volume 26, Issue 6, pp 371–385

Competitive Inhibitory Effects of Acetazolamide upon Interactions with Bovine Carbonic Anhydrase II

  • Shahrokh Safarian
  • Fatemeh Bagheri
  • Ali Akbar Moosavi-Movahedi
  • Massoud Amanlou
  • Nader Sheibani
Article

Abstract

Sulfonamide drugs mediate their main therapeutic effects through modulation of the activity of membrane and cytosolic carbonic anhydrases. How interactions of sulfonamide drugs impact structural properties and activity of carbonic anhydrases requires further study. Here the effect of acetazolamide on the structure and function of bovine carbonic anhydrase II (cytosolic form of the enzyme) was evaluated. The Far-UV CD studies indicated that carbonic anhydrase, for the most part, retains its secondary structure in the presence of acetazolamide. Fluorescence measurements using iodide ions and ANS, along with ASA calculations, revealed that in the presence of acetazolamide minimal conformational changes occurred in the carbonic anhydrase structure. These structural changes, which may involve spatial reorientation of Trp 4 and Trp 190 or some other related aminoacyl residues near the active site, considerably reduced the catalytic activity of the enzyme while its thermal stability was slightly increased. Our binding results indicated that binding of acetazolamide to the protein could occur with a 1:1 ratio, one mole of acetazolamide per one mole of the protein. However, the obtained kinetic results supported the existence of two acetazolamide binding sites on the protein structure. The occupation of each of these binding sites by acetazolamide completely inactivates the enzyme. Advanced analysis of the kinetic results revealed that there are two substrate (p-NPA) binding sites whose simultaneous occupation is required for full enzyme activity. Thus, these studies suggest that the two isoforms of CA II should exist in the medium, each of which contains one substrate binding site (catalytic site) and one acetazolamide binding site. The acetazolamide binding site is equivalent to the catalytic site, thus, inhibiting enzyme activity by a competitive mechanism.

Keywords

Bovine carbonic anhydrase II acetazolamide binding study competitive inhibition isoforms 

Abbreviations

CA

carbonic anhydrase

BCA

bovine carbonic anhydrase

HCA

human carbonic anhydrase

p-NPA

p-nitrophenylacetate

Trp

tryptophan

His

histidine

ε

extinction coefficient

ANS

anilinonaphtalene sulfonic acid

KI

potassium iodide

CD

circular dichroism

ASA

accessible surface area

mAb/min

milliabsorbance per minute

a.u.

arbitrary unit

Å2

surface unit equal to one square of Angstrom

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Shahrokh Safarian
    • 1
  • Fatemeh Bagheri
    • 1
  • Ali Akbar Moosavi-Movahedi
    • 2
  • Massoud Amanlou
    • 3
  • Nader Sheibani
    • 4
  1. 1.Department of Cell and Molecular Biology, School of BiologyUniversity College of Science, University of TehranTehranIran
  2. 2.Institute of Biochemistry & BiophysicsUniversity of TehranTehranIran
  3. 3.Faculty of PharmacologyTehran University of Medical SciencesTehranIran
  4. 4.Departments of Ophthalmology and Visual Sciences and PharmacologyUniversity of WisconsinMadisonUSA

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