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Biological Chemistry

Arsenate-Phosphate Debate Continues

Review suggests controversy should stimulate interest in studies of enzyme promiscuity

by Carmen Drahl
January 17, 2011 | APPEARED IN VOLUME 89, ISSUE 3

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Credit: Adapted from Biochemistry
X-ray structure of two arsenates (green and red) bound to the active site of the phosphate-utilizing enzyme l-aspartate-β-semialdehyde dehydrogenase (pink and blue).
Credit: Adapted from Biochemistry
X-ray structure of two arsenates (green and red) bound to the active site of the phosphate-utilizing enzyme l-aspartate-β-semialdehyde dehydrogenase (pink and blue).

A high-profile claim last month that a microbe could incorporate arsenic into its DNA spawned vociferous criticism (C&EN, Dec. 13, 2010, page 7). Now, Dan S. Tawfik of Israel’s Weizmann Institute of Science and Ronald E. Viola of the University of Toledo have written a review suggesting that even though arsenic’s chemical properties make the claim unlikely, the dispute should spur new arsenic biochemistry studies (Biochemistry, DOI: 10.1021/bi200002a). Not only would arsenic-based DNA be unstable in water, but living things that use arsenate (AsO4 3–) and phosphate (PO4 3–) would also need to evolve enzymes that can tell those two nearly identical species apart, a challenging molecular recognition problem, the authors write. Previous studies suggest that phosphate-utilizing enzymes tend to accept arsenate as an alternative substrate, although the resulting reaction products rapidly decompose. More work must be done to determine whether strict discrimination between arsenate and phosphate is possible and what protein structural features might drive selectivity, Tawfik says. Such research could provide clues about how flexible life’s chemistry can be, Viola says, adding, “we have to keep an open mind about what’s possible.”

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