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- Assarsson, Maria, et al.
(författare)
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Restoring proper radical generation by azide binding to the iron site of the E238A mutant R2 protein of ribonucleotide reductase from Escherichia coli.
- 2001
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 276:29, s. 26852-26859
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme activity of Escherichia coli ribonucleotide reductase requires the presence of a stable tyrosyl free radical and diiron center in its smaller R2 component. The iron/radical site is formed in a reconstitution reaction between ferrous iron and molecular oxygen in the protein. The reaction is known to proceed via a paramagnetic intermediate X, formally a Fe(III)-Fe(IV) state. We have used 9.6 GHz and 285 GHz EPR to investigate intermediates in the reconstitution reaction in the iron ligand mutant R2 E238A with or without azide, formate, or acetate present. Paramagnetic intermediates, i.e. a long-living X-like intermediate and a transient tyrosyl radical, were observed only with azide and under none of the other conditions. A crystal structure of the mutant protein R2 E238A/Y122F with a diferrous iron site complexed with azide was determined. Azide was found to be a bridging ligand and the absent Glu-238 ligand was compensated for by azide and an extra coordination from Glu-204. A general scheme for the reconstitution reaction is presented based on EPR and structure results. This indicates that tyrosyl radical generation requires a specific ligand coordination with 4-coordinate Fe1 and 6-coordinate Fe2 after oxygen binding to the diferrous site.
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| 7. |
- Karlsson, M, et al.
(författare)
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Initiation of Escherichia coli ribosomes on matrix coupled mRNAs studied by optical biosensor technique
- 1999
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Ingår i: BIOCHIMIE. - : EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER. - 0300-9084. ; 81:10, s. 995-1002
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The optical biosensor technique, based on the surface plasmon resonance (SPR) phenomenon, has been used to study the initiation of protein synthesis by E. coli ribosomes on surface coupled mRNA. mRNA was first periodate oxidized and then hydrazide coupled
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| 9. |
- Martinka, P, et al.
(författare)
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Adenosine increases calcium sensitivity via receptor-independent activation of the p38/MK2 pathway in mesenteric arteries
- 2008
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 193:1, s. 37-46
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Tidskriftsartikel (refereegranskat)abstract
- AIM: Adenosine (Ado) restores desensitized angiotensin II-induced contractions in the renal arterioles via an intracellular, receptor-independent mechanisms including the p38 mitogen-activated protein kinase (MAPK). In the present study we test the hypothesis that MAPK-activated protein kinase 2 (MK2) mediates the Ado effect downstream from p38 MAPK resulting in an increased phosphorylation of the regulatory unit of the myosin light chain (MLC(20)). METHODS AND RESULTS: Contraction experiments were performed in rings of mesenteric arteries under isometric conditions in C57BL6 and MK2 knock out mice (MK2-/-). Ado pretreatment (10(-5) mol L(-1)) strongly increased Ang II sensitivity, calcium sensitivity and the phosphorylation of MLC(20). Treatment with Ado (3 x 10(-6) or 10(-5) mol L(-1) in between successive Ang II applications) enhanced the desensitized Ang II responses (second to fifth application). Ca(2+) transients were not effected by Ado. Further, blockade of type 1 and type 2 Ado receptors during treatment did not influence the effect. Type 3 receptor activation by inosine instead of Ado had no effect. Conversely, inhibition of nitrobenzylthioinosine-sensitive Ado transporters prevented the effects of Ado. Inhibition of p38 MAPK as well as use of MK2-/- mice prevented contractile Ado effects on the mesenteric arteries and the phosphorylation of MLC(20). CONCLUSION: The study shows that Ado activates the p38 MAPK/MK2 pathway in vascular smooth muscle via an intracellular action, which results in an increased MLC(20) phosphorylation in concert with increased calcium sensitivity of the contractile apparatus. This mechanism can significantly contribute to the regulation of vascular tone, e.g. under post-ischaemic conditions.
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| 10. |
- Müser, M. H., et al.
(författare)
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Meeting the Contact-Mechanics Challenge
- 2017
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Ingår i: Tribology letters. - : Springer New York LLC. - 1023-8883 .- 1573-2711. ; 65:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adhesion between indenter and substrate, were specified so that diverse quantities of interest, e.g., the distribution of interfacial stresses at a given load or the mean gap as a function of load, could be computed and compared to a reference solution. Many different solution strategies were pursued, ranging from traditional asperity-based models via Persson theory and brute-force computational approaches, to real-laboratory experiments and all-atom molecular dynamics simulations of a model, in which the original assignment was scaled down to the atomistic scale. While each submission contained satisfying answers for at least a subset of the posed questions, efficiency, versatility, and accuracy differed between methods, the more precise methods being, in general, computationally more complex. The aim of this paper is to provide both theorists and experimentalists with benchmarks to decide which method is the most appropriate for a particular application and to gauge the errors associated with each one..
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