Top‐down mass spectrometry of intact phosphorylated β‐casein: Correlation between the precursor charge state and internal fragments

Phosphorylated proteins play essential roles in many cellular processes, and identification and characterization of the relevant phosphoproteins can help to understand underlying mechanisms. Herein, we report a collision‐induced dissociation top‐down approach for characterizing phosphoproteins on a quadrupole time‐of‐flight mass spectrometer. β‐casein, a protein with two major isoforms and five phosphorylatable serine residues, was used as a model. Peaks corresponding to intact β‐casein ions with charged states up to 36⁺ were detected. Tandem mass spectrometry was performed on β‐casein ions of different charge states (12⁺, and 15⁺ to 28⁺) in order to determine the effects of charge state on dissociation of this protein. Most of the abundant fragments corresponded to y, b ions, and internal fragments caused by cleavage of the N‐terminal amide bond adjacent to proline residues (Xxx‐Pro). The abundance of internal fragments increased with the charge state of the protein precursor ion; these internal fragments predominantly arose from one or two Xxx‐Pro cleavage events and were difficult to accurately assign. The presence of abundant sodium adducts of β‐casein further complicated the spectra. Our results suggest that when interpreting top‐down mass spectra of phosphoproteins and other proteins, researchers should consider the potential formation of internal fragments and sodium adducts for reliable characterization.     

不对称强阻尼反应中超重碎块的产生

用改进的量子分子动力学模型研究了原子核强阻尼反应232Th +250 Cf。在入射能量范围从800-2000 MeV时,研究了反应产生的原子序数大于等于114的超重碎块的几率随入射能量的依赖情况。计算发现在不对称的强阻尼反应体系232Th +250 Cf 中超重碎块的产生几率高于在对称反应244Pu +244Pu 和 238U +238U 中超重碎块的产生几率。计算表明初级碎块的质量（电荷）分布和超重碎块的激发能分布也强烈依赖于入射能量。研究了强阻尼反应产物的衰变过程：两种不同的衰变斜率表示不同的衰变机制。它们分别相应于巨复合体系的衰变和巨复合体系的衰变碎块包括超重碎块的衰变（包含发射中子、质子和其他轻带电粒子及裂变过程）。超重碎块的衰变斜率明显低于巨复合体系的衰变斜率,可能有助于超重碎块的存活。     

中能区类弹碎片中质比的靶核相关性

基于实验测量并结合模型分析,讨论了中能区重离子周边碰撞过程中出射的类弹碎片(PLF)的中质比(N/Z)与靶核N/Z相关现象的产生原因.     

Luminescence of Ytterbium in Complexes with Cryptands Containing Bipyridine and Biisoquinoline Fragments

Some characteristics of 4fluminescence of an ytterbium ion with cryptands containing bipyridine and biisoquinoline fragments have been studied for the first time. The relationship has been established between the changes in these characteristics and the structure of a macrocyclic ligand in H₂O and D₂O at 295 and 77 K. It is shown that the highest intensities and lifetimes of 4fluminescence are observed in those complexes where a lanthanide ion is most effectively protected against water molecules.     

Fragment Binding to Kinase Hinge: If Charge Distribution and Local pKa Shifts Mislead Popular Bioisosterism Concepts

Medicinal‐chemistry optimization follows strategies replacing functional groups and attaching larger substituents at a promising lead scaffold. Well‐established bioisosterism rules are considered, however, it is difficult to estimate whether the introduced modifications really match the required properties at a binding site. The electron density distribution and pK_a values are modulated influencing protonation states and bioavailability. Considering the adjacent H‐bond donor/acceptor pattern of the hinge binding motif in a kinase, we studied by crystallography a set of fragments to map the required interaction pattern. Unexpectedly, benzoic acid and benzamidine, decorated with the correct substituents, are totally bioisosteric just as carboxamide and phenolic OH. A mono‐dentate pyridine nitrogen out‐performs bi‐dentate functionalities. The importance of correctly designing pK_a values of attached functional groups by additional substituents at the parent scaffold is rendered prominent.     

Nuclear Magnetic Resonance Structure Elucidation of Peptide b2 Ions

Tandem mass spectrometry (MS/MS) is powerful for chemical identification but it is still insufficient for explicit ion structure determination. A strategy is introduced to elucidate MS fragment ion structures using NMR spectroscopy for the first time. In our experiments, precursor ions are dissociated at atmospheric pressure and the resulting fragment ions are identified by mass spectrometry but collected outside the mass spectrometer, making the subsequent NMR measurements possible. This new strategy has been applied to determine the chemical structure of the characteristic b₂ fragment ion, a subject of longstanding debate in MS‐based proteomics.     

量子点与人源抗谷胱甘肽单链抗体的连接与表征

用已构建的表达载体pPELB-B3, 在大肠杆菌Rosetta中可溶性表达人源抗谷胱甘肽(GSH)单链抗体B3(scFv-B3), 经Ni2+螯合亲和层析纯化后, 用点印迹法验证了其与GSH结合的特异性. 将水相合成的半导体纳米粒子(半导体量子点, QDs)在N-羟基琥珀酰亚胺(NHS)和1-乙基-3-(3-二甲基氨基丙基)碳酰二亚胺盐酸盐(EDC)的作用下, 与scFvs连接. 光谱分析和膜印迹结果表明, scFvs成功地共价连接到QDs表面, 所得的QD-scFvs复合物能够较好地识别GSH. 荧光显微镜观察QD-scFvs与人乳腺癌细胞MCF-7的作用结果, 初步判断QD-scFvs能够跨膜进入细胞.     

Some aspects of heavy ion fusion-fission dynamics

Study of heavy ion induced fusion-fission reactions at near and below barrier energies has attracted a great deal of attention in recent years, due to the observations of anomalous features in the fragment angular distributions for many target-projectile systems. Additionally there are also measurements of the fragment spin distributions and time-scales of the fusion-fission reactions, which have provided important information on the dynamics of these processes. In the present paper, the emphasis would be to highlight some of the recent experimental findings and their implications on the dynamics of the fusion-fission reactions in heavy ion collisions at near and above barrier energies.     

Bismuth-fission detectors for high energy nucleons: I. Registration characteristics

There is considerable current interest in the detection of high energy nucleons around accelerators, spallation sources, and in cosmic rays. A detector that has its principal response at nucleon-energy above 50 MeV is provided by the fission of Bi-209. The problem of limited sensitivity has been solved by: a) spark counting large detector areas, b) reducing the detector background by special counting procedures, c) using many replicates of a thin track detector between two ²⁰⁹Bi-radiators. Finally, the registration efficiency has been evaluated and determined experimentally using proton beams with energies of 100, 150, and 250 MeV.     

Automation system for optical counting of nuclear tracks

An automation system consisting of the microscope, video camera and Pentium PC with frame recorder was created. The system provides counting of nuclear tracks on the SSNTD surface with a resolution of 752 × 582 points, determination of the surface area and main axis of the track. The pattern recognition program was developed for operation in Windows 3.1 (or higher) ensuring a convenient interface with the user. In a comparison of the results on automatic track counting with the more accurate hand mode it was shown that the program enables the tracks to be detected even on images with a rather high noise level. It ensures a high accuracy of track counting being comparable with the accuracy of manual counting for densities of tracks in the range of up to 2·10⁵ tracks/cm². The automatic system was applied in the experimental investigation of uranium and transuranium elements.