July 31, 1998 CHAPEL HILL - Got any valuable documents you want to preserve for posterity? Ancestors' U.S. immigration papers? Old letters? The family tree? The Declaration of Independence? The Magna Carta?
Now, a University of North Carolina at Chapel Hill scientist says his team's research suggests the best way is to keep them not only dry, but also cool. A book, for example, that might last a century at room temperature could stay in good shape for 600 years or more if kept away from moisture and simply cooled 10 degrees Celsius. Cooling papers further would extend their shelf life even more.
"We have been studying enzyme reactions and the natural process that breaks down covalent bonds which hold together compounds corresponding to the sugar building blocks of starch and cellulose," said Dr. Richard V. Wolfenden, Alumni Distinguished professor of biochemistry and biophysics at the UNC-CH School of Medicine. "Unexpectedly, we found that the decomposition, or hydrolysis, of these bonds is extremely sensitive to changing temperature and that refrigeration should provide a singularly effective means of preserving valuable documents."
A report on the research appears in the current (July 15) issue of the Journal of the American Chemical Society. Wolfenden's co-authors are graduate student Xiangdong Lu and Dr. Gregory Young, director of the UNC Biomolecular Nuclear Magnetic Resonance Facility.
The researchers found bonds holding cellulose -- the chief component of plant cell walls - and starch together to be remarkably stable, Wolfenden said. Under normal conditions, it would take 8 million years for half the bonds in cellulose to be broken and 5 million years for half the bonds in starch to decompose. By contrast, the half-lives of the covalent bonds that join DNA - the molecular blueprints for living things -- are 170,000 years and for proteins, 400 years.
"In the presence of enzymes, however, those same reactions speed up and are completed in less time than it takes a camera shutter to open and close," the UNC-CH biochemist said. "The extreme slowness of these reactions without enzymes provides a first glimpse of the extraordinary power of enzymes as catalysts."
To determine speeds at which bonds are broken, the scientists took advantage of the fact that heat causes reactions to speed up. In the laboratory, they cooked simple compounds, with bonds representing those that join long starch and cellulose molecules, in water at extremely high temperatures for various time periods, then examined the contents to see how far the reaction had progressed. The results yielded reaction rates that could be extrapolated to room temperature, at which the rates are far too slow to measure directly, the scientist said, "even for an unusually patient graduate student."
"We found that by lowering the temperature 10 degrees Celsius, the reaction rate went down six-fold," Wolfenden said. "By dropping it another 10 degrees, say from 25 degrees Celsius to five degrees, you would have almost a 40-fold decline, so that a document that would last 100 years at room temperature would last 4,000 years in a refrigerator. The accepted lore has been that most reactions double in rate with a 10-degree rise in temperature. We are now learning that this is very far from true and that some reactions increase as much as 15-fold in rate over the same interval."
Among advantages of refrigerating documents to preserve them are that it would be less expensive and less time-consuming and would not involve any of the toxic chemicals now used, he said.
"As a practical matter, what this work means is that if you have a valuable book, the best idea is to keep it in the coolest part of your house," Wolfenden said. "Everybody knows you don't want things to be damp, but what's new is that the temperature dependence of these reactions are much higher than had been suspected.
"The theoretical importance of our work is that it indicates for the first time what a magnificent job enzymes do in speeding up these reactions. These results also indicate the magnitude of the potential sensitivity of enzyme antagonists called transition state analogues (TSAs), that take advantage of this Achilles heel."
Wolfenden's research, supported by the National Institutes of Health, has been concerned with development of TSAs. Familiar examples are the herbicide Roundup, ACE inhibitors used to treat heart patients and protease inhibitors used to control the virus that causes AIDS.
"These new results suggest that, as effective as these inhibitors are, the prospects for their improvement are brighter than we suspected," Wolfenden said.
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