The 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS (Fetzner, S., Mü ller, R., and Lingens, F. (1992) J. Bacteriol. 174, 279 -290) contains both a ferredoxin-type and a Rieske-type 2Fe2S center. These two significantly different 2Fe2S clusters were characterized with respect to their EPR spectra, electrochemical properties (Rieske-type cluster with g z ؍ 2.025, g y ؍ 1.91, g x ؍ 1.79, g av ؍ 1.91, E m ؍ ؊125 ؎ 10 mV; ferredoxin-type center with g z ؍ 2.05, g y ؍ 1.96, g x ؍ 1.89, g av ؍ 1.97, E m ؍ ؊200 ؎ 10 mV) and pH dependence thereof. X band electron spin echo envelope modulation and electron nuclear double resonance spectroscopy was applied to study the interaction of the Rieske-type center of the 2-halobenzoate 1,2-dioxygenase with 2Fe2S clusters are usually divided into two distinct groups on the basis of their EPR spectra. The ferredoxin-type 2Fe2S centers are characterized by an average g-value of g av ϭ 1.96, whereas the so-called Rieske-type 2Fe2S centers show a pronounced g-factor anisotropy with g av ϭ 1.91.For a long time, the membership in either of the two classes was considered to be correlated with significantly different redox midpoint potentials, i.e. with an E m 1 Ͻ Ϫ400 mV for the ferredoxins and an E m Ͼ ϩ260 mV for the Rieske centers of the cytochrome bc complexes, the enzymes in which such a 2Fe2S center had been discovered (Rieske et al., 1964). The midpoint potential of the Rieske centers was supposed to arise from a different coordination of the cluster compared to ferredoxintype centers.To date, crystal structures of six 2Fe2S ferredoxins are available (Tsukihara et al., 1981;Tsutsui et al., 1983;Rypniewski et al., 1991;Sussman et al., 1989;Correll et al., 1992;Jacobson et al., 1993) showing that the iron atoms are coordinated by four cysteines and are bridged by a pair of acid-labile sulfur atoms. For the Rieske centers, no x-ray structure has been solved yet. The model of the cluster suggesting a coordination via two cysteines and two histidines is supported by 15 N Q band EN-DOR experiments on the terminal oxygenase of the phthalate dioxygenase from Pseudomonas cepacia (Gurbiel et al., 1989). Resonances in the frequency range below 10 MHz were attributed to two slightly inequivalent nitrogen nuclei from histidines interacting with one of the iron ions. The hyperfine coupling constants were claimed to be too high for only dipolar interaction postulating a covalent binding between the iron atom and the histidines. Further ENDOR, ESEEM, and extended x-ray absorption fine structure studies as well as results obtained from site-specific mutagenesis were interpreted in favor of this model (Gurbiel et al., 1991;Britt et al., 1991;Shergill and Cammack, 1994a;Powers et al., 1989;Tsang et al., 1989;Davidson et al., 1992).During recent years, the discovery of several "odd" systems weakened the clearcut E m distinction between the g av ϭ 1.91 and g av ϭ 1.96 clusters. (a) 2Fe2S clusters contained in cytochrome bc complexes involved in oxidation ...
The self-diffusion coefficient of sucrose in molasses, D mol , has been determined via the pulsedfield-gradient 13 C NMR technique at 25, 50, 80, and 100 °C and a dry matter content of up to 80% w/w. For this purpose 10% sucrose containing 99% 13 C nuclei in the 1 position of the glucose moiety was added. A comparison of D mol with D pure of pure aqueous solutions showed D mol < D pure at the same sucrose water ratio. Viscosities of the molasses, η mol , and pure sucrose η pure solutions were measured over a wide range (1 mPa s to 5000 Pa s) and were shown to obey the empirical formula of Ge ´notelle. The friction coefficient was found to be influenced by the nonsucrose substances of the molasses, the value of the product D mol η mol being greater than that of D pure η pure at the same sucrose/water ratio, with the deviation increasing with decreasing temperature and increasing concentration. The results have significant consequences for the modeling of the technical crystallization process.
Coronary CT angiography (CCTA) suffers from a reduced diagnostic accuracy in patients with heavily calcified coronary arteries or prior myocardial revascularisation due to artefacts caused by calcifications and stent material. CT myocardial perfusion imaging (CTMPI) yields high potential for the detection of myocardial ischemia and might help to overcome the above mentioned limitations. We analysed CT single-phase perfusion using high-pitch helical image acquisition technique in patients with prior myocardial revascularisation. Thirty-six patients with an indication for invasive coronary angiography (28 with coronary stents, 2 with coronary artery bypass grafts and 6 with both) were included in this prospective study at two study sites. All patients were examined on a 2nd generation dual-source CT system. Stress CT images were obtained using a prospectively ECG-triggered single-phase high-pitch helical image acquisition technique. During stress the tracer for myocardial perfusion (MP) SPECT imaging was administered. Rest CT images were acquired using prospectively ECG-triggered sequential CT. MP-SPECT imaging and invasive coronary angiography served as standard of reference. In this heavily diseased patient cohort CCTA alone showed a low overall diagnostic accuracy for detection of hemodynamically relevant coronary artery stenosis of only 31% on a per-patient base and 60% on a per-vessel base. Combining CCTA and CTMPI allowed for a significantly higher overall diagnostic accuracy of 78% on a per-patient base and 92% on a per-vessel base (p < 0.001). Mean radiation dose for stress CT scans was 0.9 mSv, mean radiation dose for rest CT scans was 5.0 mSv. In symptomatic patients with known coronary artery disease and prior myocardial revascularization combining CCTA and CTMPI showed significantly higher diagnostic accuracy in detection of hemodynamically significant coronary artery stenosis when compared to CCTA alone.
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