NEWS OF THE WEEK SCIENCE
SURVIVING IN AN ACID BATH Crystal structure sheds light on acid resistance of H. pyloriurease
in ammonia, the en zyme, and H. pylori, survives pH 3. The neutral lay er is easily de stroyed by vigor ous agitation or the presence of a strongly buffered acidic solution, whichfitswith the view that the en zyme is acid labile. But that view comesfromex periments using vigorous agi tation or strongly buffered solu tions, which would not let pH rise when ammonia is formed. "However, gastric juice is un buffered, and the enzyme will sel dom find itself vigorously float ing in the stomach," Oh says. "Therefore, under physiological conditions, the enzyme is acidstable, largely by virtue of its exquisite molecular design."—
HE ULCER-CAUSING BACTEmers assemble into a sphere en ria called Helicobacterpylori closing a cavity and containing 12 COURTESY OF fascinate researchers. These evenly distributed catalytic sites BYUNG-HA OH bacteria live in human stomachs, and 10 holes. which once were thought un ACID-PROOF Inside the cell, the enzyme's inhabitable because of the ex cavity is filled with cell fluid, The four trimeric tremely acidic conditions they which has buffering capacity. assemblies of harbor. Helicobacter pylori "That will protect the enzyme urease (the fourth, at H. pylori's survival in the gut is temporarily at the time of re the back of the known to be due to its high pro lease," Oh explains. Gradually, figure, is omitted for duction of urease. When this en the cavity is filled with ammonia clarity) cooperatively zyme hydrolyzes urea, the am as urea in the gastric fluid is hyrelease ammonia to monia formed neutralizes the drolyzed. The 10 holes in the form a protective acidity around the bacterium, cre sphere allow diffusion of cell neutral layer around ating a livable microenvironment. fluid and of ammoniafromactive the enzyme. Now, the crystal structure of//. sites over the sphere. Shrouded MAUREEN R0UHI pylori urease is providing more clues to the bacteria's survival tac B U S I N E S S tics. The structure was obtained recently by Byung-Ha Oh and coworkers at Pohang University 1 of Science & Technology and at he straw-based construction board in bringing environmentally conserving wood Catholic University of Daegu, business has hit a rough spot, but don't replacement panels more into the mainstream both in South Korea [Nat. Struct. tell that to Dow Chemical. with consumers." Biol, 8,505(2001)}. Dow has agreed to acquire most of Isobord, However, not everyone agrees that straw Unlike other ureases, H.pylori a Canadian company that makes a plywood panels are environmentally preferable. A urease molecules reside both in replacement out of wheat straw and methyl recent analysis by BASF, a Dow competitor in side the cytoplasm and on the cell ene diphenyl isocyanate (MDI) resin. Isobord the MDI business, found them to offer no envi surface. The surface molecules entered the strawboard business in 1998 with ronmental advantage and to be somewhat come from spontaneous lysis of a $100 million plant based on resin supplied more expensive to make (C&EN, April 2, page other H.pylori, which releases ure by Dow. However, the company ran into trou 361.-MICHAEL MCCOY ases that then adsorb onto the ble and declared bankruptcy in February of surface of intact bacteria. Scien this year. tists have believed that surface Brad Money, the Dow executive who will urease protects H. pylori against lead the acquired business, says Isobord fits strong acid, but it wasn't clear how well with Dow's position in other home con The current work proves that the struction markets. "We have always believed in enzyme survives outside the cell the product, and we continue to believe that it under the usual acidic conditions has the potential for strong commercial appeal in the stomach. The Korean re with consumers and contractors," he says. searchers credit this survival to The main appeal of Isobord over plywood is the enzyme's architecture. that it is based on an annually renewable Theyfindthat H.pylori urease resource that otherwise would be burned. has two subunits: a 61.7-kilodal- Also, because the Isobord binder doesn't con ton unit called a and a 26.5-kDa tain formaldehyde, it sidesteps a potential REPLACEMENT Isobord's environ unit called p. Three of each of health concern. Home Depot welcomed Dow's mentally friendly strawboard replaces these subunits form a triangular purchase, predicting it will be "a strong factor plywood in home construction. assembly (ap)3. Four (a0)3 tri-
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Dow Picks Up Plywood Stand-in
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