22,976 research outputs found
Spectroscopic and theoretical approaches for studying radical reactions in class I ribonucleotide reductase
Ribonucleotide reductases (RNRs) catalyze the production of deoxyribonucleotides, which are essential for DNA synthesis and repair in all organisms. The three currently known classes of RNRs are postulated to utilize a similar mechanism for ribonucleotide reduction via a transient thiyl radical, but they differ in the way this radical is generated. Class I RNR, found in all eukaryotic organisms and in some eubacteria and viruses, employs a diferric iron center and a stable tyrosyl radical in a second protein subunit, R2, to drive thiyl radical generation near the substrate binding site in subunit R1. From extensive experimental and theoretical research during the last decades, a general mechanistic model for class I RNR has emerged, showing three major mechanistic steps: generation of the tyrosyl radical by the diiron center in subunit R2, radical transfer to generate the proposed thiyl radical near the substrate bound in subunit R1, and finally catalytic reduction of the bound ribonucleotide. Amino acid- or substrate-derived radicals are involved in all three major reactions. This article summarizes the present mechanistic picture of class I RNR and highlights experimental and theoretical approaches that have contributed to our current understanding of this important class of radical enzymes
Hadron Physics with CLAS12
Hadron spectroscopy has been an essential part of the physics program with
the CLAS detector in experimental Hall B at Jefferson Lab. Production of baryon
and meson resonances with high energy (polarized) electron and photon beams was
studied on a veriety of targets, ranging from hydrogen to lead. Physics topics
of interest include: investigation of the spectrum of baryon and meson
resonances, transition form-factors, meson-nucleon couplings (mesons in
nuclei), and search for exotic and missing states. With the 12 GeV upgrade of
the CEBAF machine, hadron spectroscopy in Hall B will be extended to a new
domain of higher mass resonances and the range of higher transferred momentum
using up to 11 GeV electron beams and the upgraded CLAS12 detector. In this
paper a brief description of the CLAS12 detector and the physics program
adopted for 12 GeV with emphasis to baryon and meson spectroscopy is presented.Comment: Hadron-09 proceedings, 8 pages, 5 figure
Towards robots reasoning about group behavior of museum visitors: leader detection and group tracking
The final publication is available at IOS Press through http://dx.doi.org/10.3233/AIS-170467Peer ReviewedPostprint (author's final draft
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