|
|
 |
|
The National Academy of Sciences has chosen Professor JoAnne Stubbe, Novartis Professor of Chemistry and Professor of Biology to receive the National Academy of Sciences Award in Chemical Sciences. The prize and medal is given for innovative research in the chemical sciences that, in the broadest sense, contributes to the better understanding of the natural sciences and to the benefit of humanity. It will be presented to Professor Stubbe "for landmark work on the mechanisms and regulation of ribonucleotide reductases, a compelling demonstration of the power of chemical investigations to solve problems in biology." The award, supported by the Merck Company Foundation, has been presented since 1979. |
 |
|
The Ting lab is interested in developing new site-specific reactions for protein labeling, using enzymes that recognize an acceptor sequence with exquisite specificity but that can utilize unnatural probes with useful bioorthogonal functional groups for labeling, such as azides and alkynes. We cloned, expressed, and purified biotin ligases from nine different species, and screened them for the ability to ligate unnatural analogues of biotin onto a specific lysine residue of the human p67 biotin acceptor protein. Unique among our panel, the biotin ligases of Saccharomyces cerevisiae (yeast) and Pyrococcus horikoshii accept alkyne and azide derivatives of biotin, respectively. These new ligation reactions demonstrate the differential substrate specificities of biotin ligases from different organisms and could be useful for new protein labeling applications.
Journal of the American Chemical Society 2008, 130, 1160-1162.
S. A. Slavoff, I. Chen, Y.-A. Choi, and A. Y. Ting. |
 |
|
These images show macrophages infected with anthrax. The fluorescent green areas indicate the presence of nitric oxide (NO). In the top two panels, the anthrax can produce NO. At top left, an image taken two hours after infection shows that NO is present. These cells die. At 18 hours, top right, more NO is present, produced by the macrophages. In the bottom two panels, the anthrax infecting the macrophages is unable to produce NO. At bottom left, after two hours, almost no NO is present, but it is present (produced by the macrophages) at 18 hours, bottom right. These cells are viable.
Konstantin Shatalin*, Ivan Gusarov*, Ekaterina Avetissova*, Yelena Shatalina*, Lindsey E. McQuade†, Stephen J. Lippard† and Evgeny Nudler*
*Department of Biochemistry, New York University School of Medicine, New York, NY 10016;
†Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
|
 |
|
New Mechanism for Energy Flow in Polyatomic Molecules
Professor Robert W. Field and his group, along with collaborators at the University of Amsterdam, have observed quantum interference effects in the spectrum of acetylene that reveal a new mechanism for Inter-System Crossing (ISC) in polyatomic molecules. Most chemically stable molecules have a triplet state as their first excited electronic state. As a result, the low-lying vibrational levels of an electronically excited singlet electronic state, S1, are embedded in an ergodic manifold of highly excited vibrational levels of the lower-lying triplet state, T1. Spin-orbit S1~T1 mixing induces energy flow from the ‘optically bright’ singlet state into the dense bath of ‘optically dark’ triplet vibrational states in a process known as Inter-System Crossing (ISC). The traditional model for ISC in polyatomic molecules is a statistical decay mechanism, where there is no explicit causality in the flow of energy from one electronic state to the next. The Field group and collaborators have obtained evidence in support of a new, deterministic model called the ‘doorway mechanism’ of ISC. In the ‘single doorway’ mechanism, rather than a pure statistical decay, ISC is promoted by a special doorway state that can uniquely facilitate coupling of an S1 state into the bath of indistinguishable T1 vibrational states. The ‘double doorway’ mechanism involves two doorway-mediated paths between the bright state (S1) and dark bath (T1). These two paths can interfere with each other, giving rise to quantum interference effects that are observable in the molecular spectrum. State-resolved photoelectron spectroscopy (U of Amsterdam) and Surface Electron Ejection by Laser-Excited Metastables (SEELEM) spectroscopy (MIT) were employed to observe the quantum interference effects and confirm the energy flow mechanism as double doorway. The above figure presents the simultaneously recorded SEELEM and ultraviolet laser-induced fluorescence (UV-LIF) spectra in the region of the V03K01 sub-band of the acetylene Ã1Au –  1Sg+ electronic transition. Analysis of the spectral patterns reveals the double doorway mechanism for ISC in acetylene. The double doorway mechanism and observation of quantum interference effects offers possibilities for external manipulation and control over molecular excited state dynamics and non-radiative energy flow in polyatomic molecules. |
|
|
|
|
