Characterization of a new type of sulfite dehydrogenase from Paracoccus pantotrophus GB17

The periplasmic sulfite dehydrogenase of Paracoccus pantotrophus GB17 was purified to homogeneity by a four-step procedure from cells grown lithoautotrophically with thiosulfate. The molecular mass of native sulfite dehydrogenase was 190 kDa as determined by native gradient PAGE. SDS-PAGE showed sulfite dehydrogenase to comprise two subunits with molecular masses of 47 kDa and 50 kDa, suggesting an {alpha}2{beta}2 structure. The N-terminal amino acid sequence and immunochemical analysis using SoxC-specific antibodies identified the 47-kDa protein as the soxC gene product. SoxD-specific antibodies identified the 50-kDa protein as SoxD. Based on the molecular masses deduced from the nucleotide sequence for mature SoxC (43,442 Da) and SoxD (37,637 Da) sulfite dehydrogenase contained 1.30 mol molybdenum/mol {alpha}2{beta}2 sulfite dehydrogenase. The iron content was 3.17 mol/mol α2β2 sulfite dehydrogenase, and 3.53 mol heme/mol {alpha}2{beta}2 sulfite dehydrogenase was determined by pyridine hemochrome analysis. These data are consistent with the two heme-binding domains (CxxCH), characteristic for c-type cytochromes, deduced from the soxD nucleotide sequence. Electrospray ionization revealed two masses for SoxC of 43,503 and 43,897 Da. The difference in molecular mass was attributed to the molybdenum cofactor of SoxC. For SoxD a mass of 38,815 Da was determined; this accounted for the polypeptide and two covalently bound hemes. Reconstitution of the catalytic activity of sulfite dehydrogenase required additional fractions; these eluted from Q Sepharose at 0.05, 0.25, and 0.30 M NaCl. The K(m) of sulfite dehydrogenase for sulfite was 7.0 {mu}M and for cytochrome c 19 {mu}M. Sulfite dehydrogenase activity was inhibited by sulfate and phosphate. The structural and catalytic properties make sulfite dehydrogenase from P. denitrificans GB17 distinct from sulfite oxidases of other prokaryotic or eukaryotic sources

Depth profile characterization of ultra shallow junction implants

A need for analysis techniques, complementary to secondary ion mass spectrometry (SIMS), for depth profiling dopants in silicon for ultra shallow junction (USJ) applications in CMOS technologies has recently emerged following the difficulties SIMS is facing there. Grazing incidence X-ray fluorescence (GIXRF) analysis in the soft X-ray range is a high-potential tool for this purpose. It provides excellent conditions for the excitation of the B-K and the As-L iii,ii shells. The X-ray standing wave (XSW) field associated with GIXRF on flat samples is used here as a tunable sensor to obtain information about the implantation profile because the in-depth changes of the XSW intensity are dependent on the angle of incidence. This technique is very sensitive to near-surface layers and is therefore well suited for the analysis of USJ distributions. Si wafers implanted with either arsenic or boron at different fluences and implantation energies were used to compare SIMS with synchrotron radiation-induced GIXRF analysis. GIXRF measurements were carried out at the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II using monochromatized undulator radiation of well-known radiant power and spectral purity. The use of an absolutely calibrated energy-dispersive detector for the acquisition of the B-Kα and As-Lα fluorescence radiation enabled the absolute determination of the total retained dose. The concentration profile was obtained by ab initio calculation and comparison with the angular measurements of the X-ray fluorescence

Colloquium Spectroscopicum Internationale XXIV. Book of abstracts. Vol. 2

Available from Gesellschaft Deutscher Chemiker, Frankfurt am Main (Germany, F.R.). Arbeitskreis fuer Angewandte Spektroskopie (DASp) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman