Conformational changes in conantokin-G induced upon binding of calcium and magnesium as revealed by NMR structural analysis

The apo- and metal-bound solution conformations of synthetic conantokin-G (con-G, G1Egamma gammaL5Q gamma NQgamma 10LIRgamma K15SN-CONH2, gamma = gamma-carboxyglutamic acid), an antagonist of N-methyl-D-aspartate receptor-derived neuronal ion channels, have been examined by one- and two-dimensional 1H NMR at neutral pH. A complete structure for the Mg2+-loaded peptide was defined by use of distance geometry calculations and was found to exist as an alpha-helix that spans the entire peptide. The alpha-helical nature of Mg2+/con-G was also supported by the small values (<5.5 Hz) of the 3JHNalpha coupling constants measured for amino acid residues 3-5, 8, 9, and 11-16, and the small values (<4 ppb/K) of the temperature coefficients observed for the alphaNH protons of residues 5-17. This conformation contrasted with that obtained for apo-con-G, which was nearly structureless in solution. Docking of Mg2+ into con-G was accomplished by use of the genetic algorithm/molecular dynamics simulation method, employing the NMR-derived Mg2+-loaded structure for initial coordinates in the midpoint calculations. For the 3 Mg2+/con-G model, it was found that binding of one Mg2+ ion is stabilized by oxygen atoms from three gamma-carboxylates of Gla3, Gla4, and Gla7; another Mg2+ is coordinated by two oxygen atoms, one from each of the gamma-carboxylates of Gla7; and a third metal ion through three donor oxygen atoms of gamma-carboxylates from Gla10 and Gla14. As shown from direct metal binding measurements to mutant con-G peptides, these latter two Gla residues probably stabilized the tightest binding Mg2+ ion. Circular dichroism studies of these same peptide variants demonstrated that all Gla residues contribute to the adoption of the Mg2+-dependent alpha-helical conformation in con-G. The data obtained in this investigation provide a molecular basis for the large conformational alteration observed in apo-con-G as a result of divalent cation binding and allow assessment of the roles of individual Gla residues in defining certain of the structure-function properties of con-G.     

Breech delivery. Selection by X-ray pelvimetry

An attempt was made to evaluate the possible benefit of selecting women for vaginal breech delivery at term by radiological pelvimetry. Information from medical records on 276 singleton breech deliveries were analysed. A total of 188 breech presentations were diagnosed before the onset of labour, pelvimetry was performed in 74 women, where pelvic dimensions too small for recommendation of vaginal breech delivery were found in 30 cases. The overall rate of caesarean section was 78%, among diagnosed patients it was 84% and 64% among undiagnosed breech presentations. Rates of morbidity (low Apgar score and admission to the neonatal care unit) did not differ significantly between infants delivered vaginally or by elective caesarean section. The material, however, is too small for valid conclusions regarding safety of vaginal delivery of term breech in women selected by criteria including estimate of pelvic size.     

Antibiotic prophylaxis in cesarean section

BACKGROUND: To investigate the guidelines for patient selection and drug regimens for application of antibiotic prophylaxis in relation to cesarean section in the maternity clinics in Denmark. METHODS: A questionnaire to all the Danish maternity clinics that perform cesarean section, concerning indications for application of antibiotic prophylaxis and antibiotic regimens to patients undergoing acute and elective cesarean section. RESULTS: All departments (n = 48) returned the questionnaire. Twenty departments (46%) provided written guidelines for antibiotic prophylaxis. Four departments (8%) used antibiotic prophylaxis to elective cesarean sections, 25 departments (52%) applied antibiotics to all emergency sections. In the presence of the rupture of membranes or prolongation of labor (> 12 hrs) 58% and 63% of the departments applied antibiotic prophylaxis, respectively. The most infrequent first choice drug was cefuroxim, employed by 27 departments (56%). Concerning timing, 21 departments (44%) applied antibiotics after cord clamping and 13 departments (27%) before incision. CONCLUSION: We propose a nation-wide prospective investigation on the rate of infections associated with cesarean section to set up rational guidelines for antibiotic prophylaxis.     

Optimization of Pr3+:ZBLAN fiber amplifiers

Experimental parameters have been measured and used in a quantitative model of Pr³⁺-doped fluorozirconate fiber amplifiers. The optimum cutoff wavelength was determined to be 800 nm and the gain for 400 mW of pump was found to increase from 12 to 34 dB if the NA was increased from 0.15 to 0.25. Lengthening the metastable state lifetime from 110 to 300 μs would significantly improve amplifier performance while concentration quenching can appreciably degrade it     

Analysis of noise in cascaded non-linear stages

This paper presents a method to analyse noise in cascaded non-linear stages based on Volterra series for multiport systems. the cascaded stages are partitioned such that internal noise sources from different stages are uncorrelated and linear loading between all stages can be assumed. This partitioning scheme implies that the ensemble average of the magnitude-squared output response from the last stage in the cascade can be determined as a sum of noise contributions from the individual stages. the method allows both unmodulated (independent) and modulated (dependent) noise sources. A special case of the theory and two related examples are presented to illustrate the method.     

Evaluation of the 800 nm pump band for erbium-doped fiberamplifiers

Performs a comprehensive experimental and theoretical investigation of methods for overcoming the excited-state absorption (ESA), which is the main obstacle to efficient pumping of erbium-doped fiber amplifiers (EDFAs) at 800 nm. The effects of ESA on gain can be reduced at the cost of an additional noise penalty by adopting bidirectional pumping or by pumping in the long-wavelength tail of the ground-state absorption (GSA) band. The GSA and ESA cross-section spectra on the glass host material. One of the most promising hosts, fluorophosphate, is compared to Al/P silica in a detailed analysis based on a quantitative numerical model. It is predicted that 2-3 dB less pump power is required for the fluorophosphate EDFA. For Al/P-silica EDFAs, it is found that ~7-dB-higher power is required when pumping in the 800 nm band than for pumping at 980 and 1480 nm     

Effect of reactive gas mass flow on the composition and structure of AIN films deposited by reactive sputtering

The mass flow of the reactive gas during sputtering of AIN has been studied in order to control film stoichiometry as well as film structure and morphology. It has been observed that the film composition and sputtering rate depend strongly on the deposition conditions and, in particular, on the mass flow and the sputtering pressure. It has been possible to deposit transparent, almost stoichiometric as well as non-transparent, metal-rich AIN films. The metal-rich films had a sputtering rate which was a factor of six higher than that for the stoichiometric films. The crystalline texture and the morphology have been studied as a function of the total sputtering pressure for both film types. For the transparent films, this novel deposition procedure may be applied in surface acoustic wave devices. The non-transparent AIN films exhibit some similarities to films obtained by ion vapour deposition or ion-beam-enhanced deposition methods, and the films exhibit interesting tribological properties.     

Introducing the GERAN flexible layer one concept

A major enhancement of GERAN is the flexible layer one (FLO) concept, due to be introduced in Release 6 of the 3GPP standards. FLO greatly simplifies the introduction of new services to the GERAN system, allowing "tailor-made" QoS provision, significantly enhancing GERAN's flexibility and ensuring that it can continue to provide services on a par with other 3G systems. Other benefits of FLO include improved link layer performance when carrying services such as voice over IP, improved multiplexing ability, and spectral efficiency. This article introduces the FLO concept, how it works, the changes it requires, and its benefits and disadvantages.