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STANFORD - In a world where some like it hot, the life form Pyrococcus beats them all. Happiest at 100<degree>C (212<degree>F), uncomfortable at chilly 80<degree>C (176<degree>F), Pyrococcus furiosus flat-out refuses to live at temperatures as cool as summertime in Death Valley.

Pyrococcus belongs to the hyperthermophilic bacteria that dwell around the hottest underwater hydrothermal vents in the deep sea, which spit out water of 350<degree>C (662<degree>F), through holes in the Earth's crust.

Its habitat is not the only feature that makes Pyrococcus different: It also runs its metabolism with a strange set of enzymes containing the metal tungsten, an oddity in biology.

Graham George, a chemist at the Stanford Synchrotron Radiation Laboratory, uses synchrotron radiation tapped from the Stanford Linear Accelerator's SPEAR storage ring to take a closer look at these tungsten enzymes. Synchrotron radiation is extremely intense light that charged particles emit when racing on a circular path at near-relativistic speed.

"Tungsten plays almost no role in familiar organisms that we know of, but is crucial for these hyperthermophilic organisms," George said.

Although the researchers do not have practical applications in mind, they think Pyrococcus furiosus deserves attention because it is a very ancient creature that belongs to a separate kingdom of living things, called archaebacteriae.

The archaebacteriae are "the lunatics of the bacterial world," George said. "They are extremists in every possible way, from their habitats to their diet and cellular structure and workings."

While every animal from the food-spoiling bacterium Escherichia coli up to humans has cell membranes that consist of two layers of fatty acids, the archaebacteriae's membranes make do without any fatty acids at all and look more like monolayers. That make-up helps them stay intact in the heat of their environments.

In terms of cellular and membrane biochemistry, we humans are more closely related to the Escherichia coli than that bacterium is to Pyrococcus. On the evolutionary family tree of all species, the archaebacteriae branched off earlier than all other known living things. Consequently, it is believed that tungsten's use in biology might be very old, with it possibly being replaced by other elements later in development.

Employing X-ray Absorption Spectroscopy (XAS) - a method that shines strong synchrotron X-rays through solutions of metal- containing proteins and analyzes the patterns of weak rebounding waves - George and his collaborator are trying to work out the three-dimensional structure of the atoms surrounding the tungsten atoms. Knowing that structure will help the researchers determine exactly how these eccentric enzymes might function.

With Michael Adams, professor of biochemistry at the University of Georgia, George has found that sulfur and oxygen atoms most likely are the direct neighbors of a central tungsten atom. Possibly shaped like a pyramid - though the exact geometry is still unclear - these atoms form a small, inorganic center within the protein.

The behavior of tungsten is similar to the much more ubiquitous metal molybdenum. Correspondingly, George said, they found tungsten to form structures that researchers are already familiar with through earlier studies of molybdenum. The chemical similarity might partly be caused by related molecular architectures.

"This work is exciting because the tungsten enzymes are a whole new class of enzymes and yet display structural similarities with well-known molybdenum enzymes. XAS helps us understand the chemistry happening in these unusual bacterial proteins," George said.

Why tungsten is used by the hyperthermophilic bacteria, and whether it contributes to making them so well-suited to high temperatures, is not yet clear.

"We are doing this because it's novel and different," George said. "The project is still in its very early days," said George.

George joined SSRL's scientific staff last fall after having been a senior staff chemist at the Corporate Research Laboratory of Exxon Research and Engineering in Annandale, N.J.


This story was written by Gabrielle Strobel, a science writing intern at the Stanford News Service.


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