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The pterin of the molybdenum cofactor
Abstract:
The molybdenum cofactor common to a variety of molybdoenzymes has been shown to contain a novel pterin. The pterin has been isolated from sulfite oxidase from several sources, xanthine-oxidizing enzymes from milk and chicken liver, and nitrate reductase of Chlorella vulgaris after denaturation of the proteins in the presence of I2. Investigation of the anionic nature of the isolated pterin has revealed that it is a monophosphate ester susceptible to cleavage by alkaline phosphatase. Quantitative analyses have shown that one molecule of the pterin phosphate is associated with each molybdenum atom in sulfite oxidase. Studies to date have shown that the pterin is present in a reduced form in sulfite oxidase and xanthine dehydrogenase, and that in situ oxidation of the pterin leads to inactivation of sulfite oxidase.
Insights
Researchers discovered a novel pterin molecule within the molybdenum cofactor of essential enzymes. This pterin phosphate is crucial for molybdoenzyme activity and its oxidation leads to enzyme inactivation.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Molybdoenzymes are critical enzymes utilizing a molybdenum cofactor.
- The precise structure and function of this cofactor have been under investigation.
- Previous studies suggested a pterin component but lacked definitive characterization.
Purpose of the Study:
- To isolate and characterize the novel pterin component of the molybdenum cofactor.
- To investigate the role of this pterin in the function of various molybdoenzymes.
- To elucidate the relationship between the pterin structure and enzyme activity.
Main Methods:
- Isolation of the pterin from purified sulfite oxidase, xanthine-oxidizing enzymes, and nitrate reductase.
- Protein denaturation in the presence of iodine (I2) to release the cofactor.
- Analysis of the pterin's anionic nature and susceptibility to enzymatic cleavage (alkaline phosphatase).
- Quantitative analysis to determine the pterin-to-molybdenum ratio.
Main Results:
- A novel pterin was successfully isolated from multiple molybdoenzymes.
- The isolated pterin was identified as a monophosphate ester.
- A 1:1 molar ratio of pterin phosphate to molybdenum was confirmed in sulfite oxidase.
- The pterin exists in a reduced form in active enzymes and its oxidation causes inactivation.
Conclusions:
- The molybdenum cofactor contains a unique pterin monophosphate.
- This pterin is essential for the catalytic activity of molybdoenzymes.
- The redox state of the pterin directly impacts enzyme function and stability.