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Physics

Boi Hanh Huynh
Novel Reaction Intermediates in the Reaction of Toluene/o-Xylene Monooxygenase Hydroxylase I100W Variant with O2

Boi Hanh Huynh,a Leslie J. Murray,b Ricardo García-Serres,a Viviana Izzo,b Sunil Naik,a and Stephen J. Lippardb
a) Deptment of Physics, Emory University, Atlanta, GA 30322; b) Department of Chemistry, MIT, Cambridge, MA 02139; e-mail: vhuynh@emory.edu

We report the generation and characterization of reaction intermediates in a variant form of the toluene/o-xylene monooxygenase hydroxylase component (ToMOH) from Pseudomonas stuzeri OX1. Stopped-flow UV/Vis absorption, rapid freeze-quench (RFQ) electron paramagnetic resonance and RFQ Mössbauer spectroscopies were used to investigate the single turn-over reaction of chemically reduced ToMOH-I100W with O2 in the presence of the coupling protein, ToMOD. A transient species was observed in the UV/vis spectrum with an absorption maximum at 500 nm and an extinction coefficient of 1.5×103 M-1 cm-1, consistent with a neutral tryptophan radical. EPR and Mössbauer spectra of RFQ samples, together with the UV/vis data, identify this transient species as a diiron(III, IV) complex spin-coupled to a W•. A diamagnetic precursor to this diiron(III, IV)-W• was detected in the Mössbauer spectra with parameters (d= 0.54 ± 0.02 mm/s and DEQ = 0.66 ± 0.03 mm/s) that are characteristic of high-spin FeIII. We have tentatively assigned this antiferromagnetically coupled diiron(III) intermediate as a peroxo-bridged cluster. The Mössbauer parameter for this peroxodiiron(III) intermediate, however, differ from those reported for the peroxodiiron(III) species in other carboxylate-bridged diiron proteins, for which d  > 0.60 mm/s and DEQ > 1.00 mm/s. Furthermore, the peroxodiiron(III) species of these other proteins exhibit UV/vis absorption with lmax greater than 650 nm, but no such features are observed for the ToMOH-I100W intermediate. Preliminary evidence indicates that the diiron(III, IV)-W• may decay via hydroxylation of W100, and that a transient species with Mössbauer parameters identical to those of the peroxodiiron(III) intermediate in ToMOH-I100W also accumulates in the reaction of wild-type ToMOH with O2. Mechanistic implications of these observations are discussed.

Sidney Perkowitz
4I: Earth, Air, Fire, Water: Ancient Nature, Modern Environments

The 4th European Biannual Conference of the Society for Science, Literature, and the Arts - Amsterdam 13-16 June 2006

The Rarest Element: Water and Life*

Sidney Perkowitz, Charles Howard Candler Professor of Physics

One of the first Greek philosophers, Thales of Miletus, wrote "All things are water." But modern knowledge shows the opposite. Out of over 150 planets and planet-sized moons we know in the universe, only one in addition to our Earth, Jupiter's satellite Europa, is seriously thought to have liquid water. To the best of our knowledge, water is the rarest of the four classical elements. It also displays a strange and virtually unique combination of properties, including its retrograde behavior when it freezes, its molecular interactions, its ability to dissolve almost anything, and its support of the random, chaotic effects of turbulence. These odd qualities, few of which are understood, make water an essential part of the environment for life. In this talk, I'll intersperse what scientists know about water with readings from my essay "The Rarest Element" (from Writing on Water, MIT Press, 2001) to illustrate water's environmental role, and incidentally to comment on the challenges of presenting valid scientific information in literary form.

* This talk was made possible by a faculty travel grant from the Institute of Comparative and International Studies, Emory University.

It All Started with Metropolis: Scientists in Film and on Stage*

Sidney Perkowitz, Charles Howard Candler Professor of Physics

Rotwang, the wild-haired scientist-wizard who created the robot Maria in Fritz Lang’s Metropolis (1927), Dr. Frankenstein in Frankenstein (1931), and Dr. Carrington in The Thing (1951) are early examples of scientists shown on film as obsessed, mad, or fatally arrogant. Since then, many movies have portrayed scientists as caricatures. Only a few make the effort to present fully fleshed out scientific characters, showing either well-done fictional scientists like Ellie Arroway (Jodie Foster) in Contact, or real scientists, like Robert Oppenheimer in Fat Man and Little Boy or Dian Fossey in Gorillas in the Mist. The situation is different in works for the theater. Although Karel Capek’s early play R. U. R. (1920) revolves around scientific arrogance, a comparatively large number of plays, from Bertolt Brecht’s Galileo to Michael Frayn’s Copenhagen touch on real scientific lives. Using comparisons of significant films and plays, and readings from the presenter’s own play Glory Enough: Rosalind Franklin and DNA (produced 2005) this talk examines the differing portrayals of scientists in films and on stage.

* These talks were made possible by a faculty travel grant from the Institute of Comparative and International Studies, Emory University.