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Reduced thioredoxin as a sulfur-acceptor substrate for rhodanese
1Department of Biochemistry and Molecular Biology, University of Chicago, IL 60637, USA.
The International Journal of Biochemistry & Cell Biology
|October 24, 1998
Summary
Mammalian rhodanese effectively uses reduced thioredoxin as a sulfur acceptor, a finding significant for understanding sulfur metabolism and enzyme kinetics. This research identifies a new physiological substrate for this important enzyme.
Area of Science:
- Biochemistry
- Enzymology
- Sulfur Metabolism
Background:
- Mammalian rhodanese (thiosulfate: cyanide sulfurtransferase, EC 2.8.1.1) is known to transfer sulfane sulfur.
- It accepts sulfur from thiosulfate and organic thiosulfonates, and transfers it to acceptors like cyanide and dithiols.
Purpose of the Study:
- To investigate reduced thioredoxin as a potential sulfur-acceptor substrate for rhodanese.
- To characterize the kinetic parameters of rhodanese with thioredoxin and other substrates.
Main Methods:
- Utilized an NADPH-coupled assay involving thioredoxin reductase.
- Measured enzyme kinetics using varying concentrations of thioredoxin and methane thiosulfonate.
- Investigated alanine thiosulfonate as a potential donor substrate.
Main Results:
- Reduced thioredoxin was identified as an effective sulfur-acceptor substrate for rhodanese at micromolar concentrations.
- This contrasts with the millimolar concentrations required for lipoate or dithiothreitol.
- Apparent K(m) values for thioredoxin and methane thiosulfonate were determined.
- Alanine thiosulfonate was shown to function as a donor substrate.
- Inorganic sulfide accumulated as a product.
Conclusions:
- Reduced thioredoxin is a physiologically relevant and efficient sulfur acceptor for mammalian rhodanese.
- The findings expand the known substrate range for rhodanese and provide insights into sulfur transfer pathways.
- A mechanistic model for these reactions is proposed.