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Bicarbonate is a recycling substrate for cyanase.
The Journal of Biological Chemistry
|July 5, 1987
Summary
Cyanase enzyme in E. coli breaks down cyanate using bicarbonate as a substrate, producing ammonia and carbon dioxide. This study confirms bicarbonate is a recycling substrate, not water, in this enzymatic reaction.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Cyanase is an inducible enzyme in Escherichia coli.
- It catalyzes the bicarbonate-dependent decomposition of cyanate into ammonia and bicarbonate.
- Previous studies proposed a kinetic mechanism involving carbamate as an initial product and bicarbonate as a substrate.
Purpose of the Study:
- To provide direct evidence for the proposed cyanase mechanism.
- To determine the substrate and product forms of carbon dioxide/bicarbonate.
- To elucidate the role of bicarbonate and water in the cyanase reaction.
Main Methods:
- Isotopic labeling studies using 14C and 13C isotopes.
- Employing 18O-labeled water and bicarbonate.
- Analyzing products formed from cyanate and bicarbonate under various labeling conditions.
Main Results:
- Bicarbonate, not carbon dioxide, serves as the substrate for cyanase.
- Carbon dioxide is produced stoichiometrically from both bicarbonate and cyanate.
- Oxygen-18 from labeled bicarbonate is incorporated into the carbon dioxide produced from cyanate, while oxygen from water is not.
Conclusions:
- The results strongly support the proposed mechanism for cyanase.
- Cyanate decomposition by cyanase is not a hydrolysis reaction.
- Bicarbonate acts as a recycling substrate in the cyanase-catalyzed reaction.