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Vitamin E fights radicals - again and again.

Vitamin E fights radicals -- again and again

For years, researchers have puzzled over why adults appear to need so little tocopherol, better known as vitamin E. While the body employs this vitamin daily to fend off potentially damaging attacks by many potent reactive chemicals, known as free radicals, tissue levels of the vitamin are usually quite low. And adults never seem to show signs of deficiency -- even while eating diets containing little or no tocopherol. New experiments now suggest why: Certain membranes within cells can recycle the vitamin by rearming it with the vital ammunition lost in its defensive salvos.

Free radicals, possessing an unpaired electron, wreak major damage by oxidizing -- robbing an electron from -- a protein or other nearby molecule. They also threaten to set in motion a self-perpetuating chain reaction as each electron they rob transforms a molecule into an electron-hungry radical itself. Vitamin E, the body's premier antioxidant, stops this destructive chain of oxidizing reactions by donating an electron.

In the process, vitamin E also becomes a radical, but a relatively nonreactive and benign one. Vitamin E radical was thought to just decay away, but studies over the past decade have suggested otherwise. To resolve the issue, Lester Packer and his coworkers at Lawrence Berkeley (Calif.) Laboratory recently fed high vitamin-E diets to rats for three weeks, enriching tocopherol levels in their mitochondrial membranes to 20 times normal. These membranes are the main site of oxygen consumption -- and therefore, Packer reasoned, a likely site of vitamin-E rejuvenators.

After isolating these membranes, the researchers scanned them spectroscopically and for the first time directly observed vitamin-E radicals in biological materials. Next, they subjected their soup of membranes and vitamin-E radicals to an electron-donating chemical and watched as the membranes' "respiratory system" began shunting electrons around. Before long, enzymes in this system transformed the radicals back to vitamin E.

Packer's finding, while not surprising, confirms that vitamin E is recycled in living systems, says Paul B. McCay at the Oklahoma (City) Medical Research Foundation. McCay's own work, with microsomal membranes, suggests glutathione -- not the respiratory system -- donates vitamin-rejuvenating electrons there. Other studies indicate that elsewhere, including the eye (SN: 5/20/89, p.308), vitamin C may play a similar role. In other words, McCay says, "every subcellular membrane may have its own [vitamin-E recycling] mechanism."
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Author:Raloff, J.
Publication:Science News
Date:May 27, 1989
Words:386
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