Gastric lipoma: a rare cause of haematemesis.

Gastric lipomas are rare benign tumours of the stomach, representing less than 3% of all benign gastric neoplasms. They are usually asymptomatic but larger lesions can present with abdominal pain, gastric outlet obstruction and haematemesis. Malignant transformation is extremely rare. Accurate preoperative diagnosis can be established with computed tomography. Being benign, extensive surgery is not necessary and simple excision of the lesion is adequate. Small asymptomatic lesions can be followed up. We present a case of 80-year-old woman with gastric submucosal lipoma who presented with haematemesis.

Quantitative Determination of Resin Loading in Solid-Phase Organic Synthesis Using (13)C MAS NMR.

The use of quantitative carbon nuclear magnetic resonance spectroscopy ((13)C NMR) for the determination of resin loadings has been investigated. Magic angle spinning (MAS) NMR spectra have been obtained for solvent-swollen resins on a conventional 7 mm CP/MAS probe using the two pulse phase modulation (TPPM) proton decoupling sequence. Loadings of resin-bound organic compounds were evaluated via addition of tetrakis(trimethylsilyl)silane as reference or using the carbon resonances of the polymeric resin material as an internal standard. Results for several functionalized Wang and trityl resins are consistent with those obtained using well-established analytical methods. The (13)C NMR method has interesting applications in the field of solid-phase organic synthesis (SPOS), since no functional group acting as a support for the attachment of a quantifiable chromophore must be available in the material of interest.

Lysine as helix C-capping residue in a synthetic peptide.

The structure of the synthetic peptide CH3CO(Leu-Ser-Leu-Leu-Leu-Ser-Leu)3Lys-NH2 in trifluoroethanol/water 60/40 (volume ratio) was characterized by two-dimensional nmr spectroscopy. The peptide, closely related to the amphiphilic helix models designed by W. F. De-Grado and co-workers to mimic protein ion channels [(1988) Science, Vol. 240, p. 1177-1181], folds into a regular helix spanning residues 1-20. Evidence for a helix C-terminal capping conformation, involving the terminal lysine residue, was observed from Overhauser effects and checked for consistency by restrained molecular dynamics simulations. The side-chain amino group of Lys22 forms a hydrogen bond with the carbonyl of Leu18, and the distorted helical geometry of the terminal dipeptide allows the inclusion of a water bridge between the backbone NH of the Lys22 residue and the carbonyls of Leu19 and Ser20.

Template-assembled melittin: structural and functional characterization of a designed, synthetic channel-forming protein.

Template-assembled proteins (TASPs) comprising 4 peptide blocks, each of either the natural melittin sequence (melittin-TASP) or of a truncated melittin sequence (amino acids 6-26, melittin6-26-TASP), C-terminally linked to a (linear or cyclic) 10-amino acid template were synthesized and characterized, structurally by CD, by fluorescence spectroscopy, and by monolayer experiments, and functionally, by electrical conductance measurements on planar bilayers and release experiments on dye-loaded vesicles. Melittin-TASP and the truncated analogue preferentially adopt alpha-helical structures in methanol (56% and 52%, respectively) as in lipid membranes. Unlike in methanol, the melittin-TASP self-aggregates in water. On an air-water interface, the differently sized molecules can be self-assembled and compressed to a compact structure with a molecular area of around 600 A2, compatible with a 4-helix bundle preferentially oriented perpendicular to the interface. The proteins reveal a strong affinity for lipid membranes. A partition coefficient of 1.5 x 10(9) M-1 was evaluated from changes of the Trp fluorescence spectra of the TASP in water and in the lipid bilayer. In planar lipid bilayers, TASP molecules are able to form defined ion channels, exhibiting a small single-channel conductance of 7 pS (in 1 M NaCl). With increasing protein concentration in the lipid bilayer, additional, larger conductance states of up to 1 nS were observed. These states are likely to be formed by aggregated TASP structures as inferred from a strongly voltage-dependent channel activity on membranes of large area. In this respect, melittin-TASP reveals channel features of the native peptide, but with a considerably lower variation in the size of the channel states. Compared to the free peptide, template-assembled melittin has a much higher membrane activity: it is about 100 times more effective in channel formation and 20 times more effective in releasing dye molecules from lipid vesicles. This demonstrates that the lytic properties are not solely related to channel formation.