Continued From

Editors' Choice common to all three kingdoms—many, but not all, of these proteins are involved in translation—which, in the authors' view, represents the fossilized metabolic machinery of the last common ancestor of the three major lineages. — GJC

Proc. Natl. Acad. Sci. U.S.A. 102,373 (2005). chemistry

Explosive Entropy

Explosive compounds, such as nitroglycerin or trinitrotoluene (TNT), tend to decompose via highly exothermic pathways. The explosion is sustained by the enthalpy released as strong bonds (in the products) form. In contrast, Dubnikova et al. suggest that triacetone triperoxide (TATP), which explodes with power comparable to that of TNT, undergoes a cXrV

A trio of peroxide-based explosives.

nearly thermoneutral decomposition and derives explosive force entirely from the increase in entropy.As its name suggests, this compound incorporates three acetone equivalents: It is a nine-membered ring with three O atom pairs separated by isopropylidene (>C(CH3)2) groups. The authors used density functional theory to calculate decomposition rates along several pathways, beginning with the structure determined by x-ray diffraction. Comparison with experimental data suggests that exothermic oxidation of the hydrocarbon groups does not play a significant role. Instead, they conclude that the explosion is initiated by cleavage of an O-O bond and is driven by the liberation of four gaseous molecules (one ozone and three acetones) from the harmless-looking solid TATP. — JSY

J. Am. Chem. Soc. 10.1021/ja0464903 (2004). applied physics

Seeing Through Fog

Light is scattered and absorbed as it travels through turbid media such as fog, cloud, and dirty water, making it difficult to image objects that may be hidden within. Some light, however, passes through ballis-tically—that is, without loss—and capturing that ballistic light offers the potential for imaging otherwise hard-to-see objects. Zevallos et al. show that combining ultrashort pulses (130 fs) of light with a pulsed detection system (80-ps window) can improve the contrast between the buried object and the noisy background that arises from the diffuse light scattered from the surrounding turbid material;the brief window lets in most of the ballistic light and only a little of the noise, thereby providing a clearer snapshot.The ability to improve the imaging of objects normally hidden from view has a whole host of applications, from the medical imaging of biological tissue to remote sensing and underwater surveillance. — ISO

Highlighted in Science's Signal transduction Knowledge Environment

Reactivating an Actin Regulator

Control of the actin cytoskeleton is critical for many cellular processes, particularly cell motility, and the actin-depolymerizing factor cofilin is inhibited by phosphorylation. Gohla et al. have identified a protein, named chronophin, with phosphatase activity toward phospho-rylated cofilin. This enzyme is a member of the haloacid dehalogenase superfamily of phosphotransferases, which have a well-described catalytic mechanism as exemplified by the Ca2+-ATPase of sarco(endo)plasmic reticulum (see Olesen et al., Reports, 24 December 04, p. 2251) but have not previously been implicated in serine dephosphorylation in mammals. Overexpression of chronophin decreased the amount of phosphorylated cofilin in HeLa cells, whereas depletion by RNA interference increased the amounts of phosphorylated cofilin and F-actin, stabilized membrane protrusions and stress fibers, and induced abnormalities in cell division.These findings suggest that chronophin could be a therapeutic target in cases (for instance, chronophin is overexpressed in neuroblastomas) where control of the actin cytoskeleton is disrupted. — LBR

Nature Cell Biol. 7,21 (2005).

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