PubMed · 12240821
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Katherine A Kovacs. 2002-09-03. Decision rules for bone mineral density testing.. https://pubmed.ncbi.nlm.nih.gov/12240821/
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Rhodobacter capsulatus xanthine dehydrogenase (XDH) forms an (alphabeta)2 heterotetramer and is highly homologous to homodimeric eukaryotic XDHs. The crystal structures of bovine XDH and R. capsulatus XDH showed that the two proteins have highly similar folds. We have developed an efficient system for the recombinant expression of R. capsulatus XDH in Escherichia coli. The recombinant protein shows spectral features and a range of substrate specificities similar to bovine milk xanthine oxidase. However, R. capsulatus XDH is at least 5 times more active than bovine XDH and, unlike mammalian XDH, does not undergo the conversion to the oxidase form. EPR spectra were obtained for the FeS centers of the enzyme showing an axial signal for FeSI, which is different from that reported for xanthine oxidase. X-ray absorption spectroscopy at the iron and molybdenum K-edge and the tungsten LIII-edge have been used to probe the different metal coordinations of variant forms of the enzyme. Based on a mutation identified in a patient suffering from xanthinuria I, the corresponding arginine 135 was substituted to a cysteine in R. capsulatus XDH, and the protein variant was purified and characterized. Two different forms of XDH-R135C were purified, an active (alphabeta)2 heterotetrameric form and an inactive (alphabeta) heterodimeric form. The active form contains a full complement of redox centers, whereas in the inactive form the FeSI center is likely to be missing.
d- and l-captopril are competitive inhibitors of metallo-beta-lactamases. For the enzymes from Bacillus cereus (BcII) and Aeromonas hydrophila (CphA), we found that the mononuclear enzymes are the favored targets for inhibition. By combining results from extended x-ray absorption fine structure, perturbed angular correlation of gamma-rays spectroscopy, and a study of metal ion binding, we derived that for Cd(II)1-BcII, the thiolate sulfur of d-captopril binds to the metal ion located at the site defined by three histidine ligand residues. This is also the case for the inhibited Co(II)1 and Co(II)2 enzymes as observed by UV-visible spectroscopy. Although the single metal ion in Cd(II)1-BcII is distributed between both available binding sites in both the uninhibited and the inhibited enzyme, Cd(II)1-CphA shows only one defined ligand geometry with the thiolate sulfur coordinating to the metal ion in the site composed of 1 Cys, 1 His, and 1 Asp. CphA shows a strong preference for d-captopril, which is also reflected in a very rigid structure of the complex as determined by perturbed angular correlation spectroscopy. For BcII and CphA, which are representatives of the metallo-beta-lactamase subclasses B1 and B2, we find two different inhibitor binding modes.
OBJECTIVES: To determine factors influencing quantitative ultrasound (QUS) parameters of the calcaneus in a population-based sample of United Arab Emirates (UAE) women, and to compare QUS parameters of the calcaneus for healthy young UAE women with the manufacturer's reference ranges for other populations. METHODS: All subjects completed a questionnaire on reproductive and life style factors. Height and weight were measured, and body composition was determined by bioelectric impedence. Estimated bone mineral density (BMD), Speed of sound (SOS), broadband ultrasound attenuation (BUA) and quantitative ultrasound index (QUI) of the right calcaneus were determined by Sahara ultrasound. RESULTS: In premenopausal women (n=330), age, weight, body mass index (BMI), lean weight, fat weight, education, age at menarche, and number of pregnancies, correlated significantly with QUS parameters. Multiple regression analysis showed that age at menarche, number of pregnancies, and BMI, were the best predictors of QUS parameters although these factors explained only small amounts of the variance (R(2)=0.05). In postmenopausal women (n=81), age, BMI and physical activity were the best predictors of BUA (R(2)=0.35), SOS (R(2)=0.39), and QUI (R(2)=0.43). Mean estimated BMD, QUI and SOS for healthy young UAE women were significantly lower than the manufacturer's reference ranges for U.S. Caucasian, European Caucasian, and Chinese Asian healthy young women of the same age range (P<0.001 for all comparisons). Mean BUA was not significantly different, however. CONCLUSIONS: Menopausal status, age, BMI and physical activity are strong predictors of QUS parameters of the calcaneus in Arabian women. Healthy young Arabian women have lower estimated calcaneal BMD compared with the manufacturer's reference ranges for other populations.