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Epithelial ovarian cancer cells enhancetheir ability to migrateand invade through the epithelial–mesenchymal transition (EMT),resulting in cell seeding and metastasis in the peritoneal cavityand onto adjacent organ surfaces. It has been speculated that cytoskeletaldynamics, such as those of the actin filament, play a role in enhancedcell motility; however, direct evidence has not been provided. Herein,we have directly measured pico- to nanonewton-scale mechanical forcesgenerated by actin dynamics of ovarian cancer SKOV-3 cells upon bindingof integrin α5β1 to fibronectin (FN), i.e., formationof a focal adhesion, using real-time atomic force microscopy (AFM)in a force spectroscopy mode. The dendrimer surface chemistry throughwhich FN was immobilized on the AFM probe surfaces further enhancedthe sensitivity of the force measurement by 1.5-fold. Post-EMT SKOV-3cells, induced by transforming growth factor-β, generated largerfocal adhesion mechanical forces (17 and 41 nN before and after EMT,respectively) with migration faster than that of pre-EMT cells. Importantly,22% of the forces transmitted through a single FN–integrinα5β1 pair from post-EMT cells were shown to be sufficientto rupture the binding between FN and integrin α5β1 onthe cells, a result which is not observed on pre-EMT cells. This impliesthat post-EMT cells, by generating forces strong enough to break theFN–integrin binding, migrate and metastasize beyond the ovary,whereas pre-EMT cancer cells are confined in the ovary without suchforce generation. These results demonstrate quantitative and directevidence for the role of actin dynamics in the enhanced motility ofpost-EMT ovarian cancer cells, providing a fundamental insight intothe mechanism of ovarian cancer metastasis. [ABSTRACT FROM AUTHOR]

The isomers of the ManGlcNAc glycan obtained from bovine ribonuclease B have been characterized by ion mobility spectrometry-tandem mass spectrometry (IMS-MS/MS). In these experiments, [Man7 + 2Na] precursors having different mobilities are selected by ion mobility spectrometry and analyzed by MS/MS techniques in an ion trap. The fragmentation spectra obtained for various precursor ions are specific, suggesting the isolation or enrichment of different glycan isomers. One fragment ion with a mass-to-charge ratio ( m/z) of 903.8 is found to correspond to the loss of an internal mannose residue of a specific isomer. Extracted fragment ion drift time distributions (XFIDTDs) yield distinctive precursor ion drift time profiles indicating the existence of four separate isomers as proposed previously. [ABSTRACT FROM AUTHOR]

Photoexcitation (using 157 nm vacuum ultraviolet radiation) of proton-bound peptide complexes leads to water elimination and the formation of longer amino acid chains. Thus, it appears that proton-bound dimers are long-lived intermediates along the pathway to peptide formation. Product specificity can be controlled by selection of specific complexes and the incorporation of blocking groups at the N- or C-termini. The product peptide sequences are confirmed using collision-induced dissociation. [ABSTRACT FROM AUTHOR]

We report the electron capture dissociation (ECD) mass spectrometry of the third generation polyamidoamine (PAMAM) dendrimer that contains amide functionalities. The dendrimer was chosen because it offers a unique opportunity to understand the ECD behavior of the amide functionality in a framework other than peptides/proteins. In this study, PAMAM ECD was found to exhibit a fragmentation pattern strikingly different from that of ordinary peptide/protein ECD. Specifically, ECD of multiply protonated PAMAM ions gave rise to significant b •,y cleavages as well as S,E dissociations but, unexpectedly, only minor c,z • fragmentations are observed. In an effort to account for the unexpectedly different fragmentation pattern, a comparative ECD experiment on the poly(propylene imine) dendrimer in which the amide bond moiety is not available and density functional theory calculations (B3LYP/6-311 + G(d)) investigations on the model system of a charge-solvated single-repeat unit were carried out. On the basis of these results, we discuss here possible implications of intramolecular charge-solvation, energy barriers in dissociation reactions, and macromolecular properties of the dendritic molecule for understanding the reaction pathway of PAMAM ECD. [Copyright &y& Elsevier]

A new method that allows a linear drift tube to be operated as a continuous ion mobility filter is described. Unlike conventional ion mobility instruments that use an electrostatic gate to introduce a packet of ions into a drift region, the present approach uses multiple segmented drift regions with modulated drift fields to produce conditions that allow only ions with appropriate mobilities to pass through the instrument. In this way, the instrument acts as a mobility filter for continuous ion sources. By changing the frequency of the applied drift fields it is possible to tune this instrument to transmit ions having different mobilities. A scan over a wide range of drift field frequencies for a single ion species shows a peak corresponding to the expected resonance time of the ions in one drift region segment and a series of peaks at higher frequencies that are overtones of the resonant frequency. The measured resolving power increases for higher overtones, making it possible to resolve structures that were unresolved in the region of the fundamental frequency. We demonstrate the approach by examining oligosaccharide isomers, raffinose and melezitose as well as a mixture of peptides obtained from enzymatic digestion of myoglobin. [Copyright &y& Elsevier]

The reaction of o-alkynyl(oxo)benzenes I with alkynes 2 in the presence of a catalytic amount of AuCl[sub 3] in (CH[sub 2]Cl)[sub 2] at 80 °C gave the [4+2] benzannulation products, naphthyl ketone derivatives 3 and 4, in high yields. When the reaction was carried out using AuBr[sub 3] instead of AuCl[sub 3], the reaction speed was enhanced and the chemical yield was increased. On the other hand, when the reaction was carried out in the presence of a catalytic amount of Cu(OTf)[sub 2] and 1 equiv of a Brønsted acid, such as CF[sub 2]HCO[sub 2]H, in (CH[sub 2]Cl)[sub 2] at 100 °C, the decarbonylated naphthalene products 5 were obtained in high yields. Similarly, the Cu(OTf)[sub 2]-H[sub 2]O-promoted reaction of the enynals 7 with an alkyne 2 afforded the corresponding [4+2] benzannulation products, decarbonylated benzene derivatives 8, in good yields. Both AuX[sub 3]- and Cu(OTf)[sub 2]catalyzed benzannulations proceed most probably through the formation of the benzo[c]pyrylium ate complex 10, the Diels-Alder addition of alkynes 2 to the ate complex, and the resulting bicyclic pyrylium ion intermediate 12. The mechanistic difference between the AuX[sub 3] and Cu(OTf)[sub 2]-HA system is discussed. [ABSTRACT FROM AUTHOR]