Is thioredoxin the physiological vitamin K epoxide reducing agent?

Area of Science:

• Biochemistry
• Enzymology
• Cellular Biology

Background:

• Dithiothreitol is a common electron donor for vitamin K epoxide reduction in mammalian liver microsomes.
• E. coli thioredoxin and thioredoxin reductase have shown potential as alternative electron donors.
• Microsomal membrane integrity, often disrupted by detergents, is crucial for this reduction process.

Purpose of the Study:

• To investigate the role of E. coli thioredoxin and thioredoxin reductase as electron donors for mammalian liver microsomal vitamin K epoxide reduction.
• To compare the thioredoxin-dependent pathway with a previously identified salicylate-inhibitable pathway.

Main Methods:

• In vitro assays using mammalian liver microsomes.
• Employing E. coli thioredoxin and thioredoxin reductase as reducing agents.
• Utilizing detergent to disrupt microsomal membrane integrity.
• Testing known thioredoxin system inhibitors and antibodies.
• Assessing inhibition by salicylate and alternate substrates.

Main Results:

• E. coli thioredoxin and thioredoxin reductase successfully replaced dithiothreitol in supporting vitamin K epoxide reduction.
• This thioredoxin-mediated activity required detergent-induced disruption of microsomal membranes.
• The salicylate-inhibitable pathway was not affected by thioredoxin system inhibitors, alternate substrates, or anti-thioredoxin antibodies.

Conclusions:

• E. coli thioredoxin and thioredoxin reductase can serve as functional electron donors for microsomal vitamin K epoxide reduction.
• The mechanism of electron transfer via the thioredoxin system differs from the previously characterized salicylate-inhibitable pathway.
• These findings highlight distinct routes for electron transfer in microsomal vitamin K metabolism.