Quantitative assessment of cysteine and cystine in peptides and proteins following organomercurial derivatization and analysis by matrix-assisted laser desorption ionization mass spectrometry

Protocols for the analysis of the sulfhydryl content in peptides and proteins using chemical derivatization by organomercurial reagents and analysis by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) have been developed. The number of reactive cysteine residues in peptides and proteins can be determined by exploiting the affinity and selectivity of organomercurial reagents for macromolecular thiols. Mass shifts observed in MALDI mass spectra obtained before and after cysteine derivatization with p-hydroxy-mercuribenzoate (pHMB) permit the number of free sulfhydryl groups to be determined. The pHMB derivative of each free cysteine residue provides a mass shift of 321 u, overcoming limitations in the mass resolution of MALDI time-of-flight mass spectrometry. Reactive cysteine residues in a macromolecule can be selectively derivatized by using a fivefold molar excess of pHMB reagent. Total sulfhydryl content (i.e., cysteine and cystine) can be determined after disulfide reduction. However, analyses for total cysteine content are more complex, requiring protein denaturation, cystine reduction, and sample purification before derivatization and analysis by MALDI-MS. Conditions for sample denaturation, alkyl-phosphine reduction, pHMB derivatization, and sample purification by analyte adsorption and desalting on protein transfer membranes, are described for cysteine/cystine analysis performed on microgram (10–200 pmol) quantities of somatostatin, insulin, hemoglobin, and β-lactoglobulin.     

100-Gb/s undersea transmission with high spectral efficiency using pre-filtered QPSK modulation format

We provide a review of our recent 100-Gb/s, high spectral efficiency (SE) experiment targeting transoceanic and regional undersea transmission distances. We demonstrated that simple pre-filtering at the transmitter together with a maximum a posteriori probability (MAP) detection algorithm can significantly improve SE. We transmitted 96×100-Gb/s pre-filtered polarization division multiplexed return-to-zero quadrature phase shift keyed (PDM-RZ-QPSK) channels with 300% SE over 10608 km using 52-km spans of 150-μm 2 fiber and simple single-stage erbium-doped fiber amplifiers (EDFAs). We also achieved 400% SE over 4368 km using similar techniques.     

Magnetism and superconductivity in ErNi2B2C

We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal ErNi₂B₂C. The incommensurate magnetic structure develops additional even harmonics below the ‘ferromagnetic’ ordering temperature, T _F of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and harmonic content. Studies of the vortex lattice show the presence of a 45° reorientation transition and a distorted hexagonal to square transition as a function of applied field. Further distortions of the vortex lattice occur at T _N, but no changes are seen at T _F.     

Critical petermann K factor for intensity noise squeezing

We investigate the impact of the Petermann-excess-noise factor K>/=1 on the possibility of intensity noise squeezing of laser light below the standard quantum limit. Using an N-mode model, we show that squeezing is limited to a floor level of 2(K-1) times the shot noise limit. Thus, even a modest Petermann factor significantly impedes squeezing, which becomes impossible when K>/=1.5. This appears as a serious limitation for obtaining sub-shot-noise light from practical semiconductor lasers. We present experimental evidence for our theory.