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Is cyanate a carbonic anhydrase substrate?
C T Supuran1, C W Conroy, T H Maren
1Universita degli Studi di Firenze, Dipartimento di Chimica, Florence, Italy.
Proteins
|February 1, 1997
Summary
This study experimentally proves that cyanide, cyanate, and thiocyanate anions are not substrates for carbonic anhydrase (CA) isozymes. It resolves controversy regarding anion binding in the enzyme active site.
Area of Science:
- Biochemistry
- Enzyme kinetics
- Bioinorganic chemistry
Background:
- Carbonic anhydrase (CA) isozymes are crucial metalloenzymes involved in various physiological processes.
- A debate exists regarding the interaction of specific anions (cyanide, cyanate, thiocyanate) with the active site of CA II, with conflicting crystallographic and spectroscopic data.
- Previous theoretical studies failed to resolve this controversy, suggesting these anions could be CA substrates.
Purpose of the Study:
- To experimentally investigate the catalytic activity of diverse carbonic anhydrase isozymes (native Zn and cobalt-substituted) towards cyanide, cyanate, and thiocyanate hydrolysis.
- To resolve the existing controversy between crystallographic and spectroscopic data concerning the binding of these anions to the CA II active site.
- To elucidate the precise mode of binding of small molecules within the enzyme active site.
Main Methods:
- Enzymatic assays were performed using various carbonic anhydrase isozymes, including native Zn- and cobalt-substituted forms.
- Kinetic studies were conducted to assess the hydrolysis rates of cyanide, cyanate, and thiocyanate in the presence of CA.
- Analysis of experimental data to determine substrate-like behavior of the investigated anions.
Main Results:
- Experimental evidence demonstrated that cyanide, cyanate, and thiocyanate do not act as substrates for any of the tested carbonic anhydrase isozymes.
- The study provides a clear experimental refutation of the hypothesis that these anions are hydrolyzed by CA.
- An explanation for the observed controversy between crystallographic and spectroscopic data was proposed, focusing on the binding mechanisms of small molecules.
Conclusions:
- Cyanide, cyanate, and thiocyanate are definitively not substrates for carbonic anhydrase isozymes.
- The findings clarify the interaction of these specific anions with the enzyme's active site, resolving long-standing debate.
- Understanding the binding modes of small molecules in enzyme active sites is critical for enzyme mechanism elucidation.