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Photodissociation Dynamics of the Thiophenoxy Radical at 248, 193, and 157 nm
Harrison, Aaron W.,Lim, Jeong Sik,Ryazanov, Mikhail,Wang, Gregory,Gao, Shumin,Neumark, Daniel M. American Chemical Society 2013 The journal of physical chemistry. A, Molecules, s Vol.117 No.46
<P>The photodissociation dynamics of the thiophenoxy radical (C<SUB>6</SUB>H<SUB>5</SUB>S) have been investigated using fast beam coincidence translational spectroscopy. Thiophenoxy radicals were produced by photodetachment of the thiophenoxide anion followed by photodissociation at 248 nm (5.0 eV), 193 nm (6.4 eV), and 157 nm (7.9 eV). Experimental results indicate two major competing dissociation channels leading to SH + C<SUB>6</SUB>H<SUB>4</SUB> (o-benzyne) and CS + C<SUB>5</SUB>H<SUB>5</SUB> (cyclopentadienyl) with a minor contribution of S + C<SUB>6</SUB>H<SUB>5</SUB> (phenyl). Photofragment mass distributions and translational energy distributions were measured at each dissociation wavelength. Transition states and minima for each reaction pathway were calculated using density functional theory to facilitate experimental interpretation. The proposed dissociation mechanism involves internal conversion from the initially prepared electronic excited state to the ground electronic state followed by statistical dissociation. Calculations show that SH loss involves a single isomerization step followed by simple bond fission. For both SH and S loss, C–S bond cleavage proceeds without an exit barrier. By contrast, the CS loss pathway entails multiple transition states and minima as it undergoes five membered ring formation and presents a small barrier with respect to products. The calculated reaction pathway is consistent with the experimental translational energy distributions in which the CS loss channel has a broader distribution peaking farther away from zero than the corresponding distributions for SH loss.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2013/jpcafh.2013.117.issue-46/jp403229h/production/images/medium/jp-2013-03229h_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp403229h'>ACS Electronic Supporting Info</A></P>
Kim, Junil,Kim, Tae-Geon,Jung, Sung Hoon,Kim, Jeong-Rae,Park, Taesung,Heslop-Harrison, Pat,Cho, Kwang-Hyun Oxford University Press 2008 Bioinformatics Vol.24 No.13
<P>MOTIVATION: Gene regulatory networks (GRNs) govern cellular differentiation processes and enable construction of multicellular organisms from single cells. Although such networks are complex, there must be evolutionary design principles that shape the network to its present form, gaining complexity from simple modules. RESULTS: To isolate particular design principles, we have computationally evolved random regulatory networks with a preference to result either in hysteresis (switching threshold depending on current state), or in multistationarity (having multiple steady states), two commonly observed dynamical features of GRNs related to differentiation processes. We have analyzed the resulting evolved networks and compared their structures and characteristics with real GRNs reported from experiments. Conclusion: We found that the artificially evolved networks have particular topologies and it was notable that these topologies share important features and similarities with the real GRNs, particularly in contrasting properties of positive and negative feedback loops. We conclude that the structures of real GRNs are consistent with selection to favor one or other of the dynamical features of multistationarity or hysteresis. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.</P>
Van Nguyen, T.,Lee, J.,Sweredoski, Michael J.,Yang, S.J.,Jeon, S.J.,Harrison, Joseph S.,Yim, J.H.,Lee, S.,Handa, H.,Kuhlman, B.,Jeong, J.S.,Reitsma, Justin M.,Park, C.S.,Hess, S.,Deshaies, Raymond J. Cell Press 2016 Molecular cell Vol.61 No.6
<P>Cereblon (CRBN), a substrate receptor for the cullin-RING ubiquitin ligase 4 (CRL4) complex, is a direct protein target for thalidomide teratogenicity and antitumor activity of immunomodulatory drugs (IMiDs). Here we report that glutamine synthetase (GS) is an endogenous substrate of CRL4(CRBN). Upon exposing cells to high glutamine concentration, GS is acetylated at lysines 11 and 14, yielding a degron that is necessary and sufficient for binding and ubiquitylation by CRL4 CRBN and degradation by the proteasome. Binding of acetylated degron peptides to CRBN depends on an intact thalidomide-binding pocket but is not competitive with IMiDs. These findings reveal a feedback loop involving CRL4 CRBN that adjusts GS protein levels in response to glutamine and uncover a new function for lysine acetylation.</P>