IOWA CITY, Iowa -- Proteins are responsible for everything from producing cell and organ structure to providing the body with nutrition. Careful regulation of their activity helps maintain essential actions such as a regular heartbeat, proper lung function, and communication among brain cells.
A mechanism that regulates protein activity, previously undescribed for advanced cells, has been reported by Dr. Toshinori Hoshi, University of Iowa assistant professor of physiology and biophysics.
The mechanism involves adding an oxygen molecule to methionine, an amino acid, in a process called oxidation. Oxidation drastically changes the way methionine interacts with its environment. The regular action of methionine is restored in a process called reduction. Unlike other amino acids, the methionine reduction, or restoration, process is carefully controlled by an enzyme. This enzyme is called MsrA.
Hoshi hypothesized that the tight control of the oxidation-reduction process in methionine might make it an important regulatory mechanism for various body functions. To test this idea, he looked at the effect methionine oxidation and reduction had on potassium channels.
Potassium channels work in the classic ball-and-chain model of opening and closing where a ball-like structure physically occludes the channel pore, closing it. Using the patch-clamp technique in combination with recombinant DNA techniques, Hoshi and his colleagues found that the oxidation and reduction of methionine did affect potassium channel activity. They found that the channel stayed open when the methionine was oxidated and closed with reduction of the amino acid. These findings are published in the September issue of the Proceedings of the National Academy of Sciences.
Hoshi thinks that these results show that the methionine oxidation-reduction process plays an important role in the regulation of potassium channels. But, he believes the regulatory mechanism plays a bigger role in body function.
"We used the potassium channels as a model to show the importance of methionine oxidation," he says. "I think it is important for every cell, and may work on all proteins, not just cell channels."
Potential importance of these findings expands beyond cell activity to cell death. There is a suggestion that methionine oxidation is involved Alzheimer's disease and aging.
"Active cells produce free radicals, molecules known to damage cells, and the enzyme, MsrA, eliminates the damage done by free radicals," he says.
Therefore, it is likely that the methionine oxidation and reduction process has antioxidant properties.
Hoshi and his colleagues are now investigating how methionine oxidation is involved in a wide variety of physiological processes, such as learning, memory and aging.
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