[Malignant phyllodes tumour : a case report].

A 28 year old woman has suffered over the previous month from a post-traumatic swelling sensation of the left breast. Ultrasonography demonstrates a 9 cm, sharply-cut, rounded, hypo-echogenic lesion. Surgery is performed, with the hypothesis of an haematoma.

Tandem mass spectrometric characterization of a specific cysteic acid residue in oxidized human apoprotein B-100.

The oxidation of low density lipoprotein (LDL) in vivo may result in its unregulated uptake by macrophages, with the consequent accumulation of cholesterol that is characteristic of the development of atherosclerosis. This paper describes initial experiments to elucidate structural changes that occur in an in vitro model of LDL oxidation. LDL was isolated from human blood and oxidized in the presence of copper ion.

Determination of high-energy fragmentation of protonated peptides using a beqq hybrid mass spectrometer.

A hybrid tandem instrument of BEqQ geometry was used to determine high-energy decomposition of protonated peptides, such as side-chain fragmentation yielding d n and w n ions. The transmission through both E and Q of such product ions, formed in the second field-free region, permits improved mass resolution and confident mass assignment. The experimental technique may involve synchronous scanning of E and Q, or, for the purpose of identification of specific products, limited-range scanning of either E or Q with the other analyzer fixed.

Decompositions of cationized heterodimers of amino acids in relation to charge location in peptide ions.

The unimolecular decompositions of protonated heterodimers of native and derivatized amino acids to yield the protonated monomers were studied as a guide to charge location in peptide ions. Analyses using a hybrid instrument of BEqQ geometry demonstrated the advantages (with respect to mass resolution, sensitivityr reproducibility, and the elimination of extraneous signals) of the detection of product ions formed in the radiofrequency-only quadrupole region (q) rather than in the field-free region between Band E. Conversion of arginine to dimethylpyrimidylomithine (DMPO) reduced the proton affinity, as evidenced by the decomposition of the protonated arginine/DMPO heterodimer.

Charge promotion of low-energy fragmentations of peptide ions.

We have examined the hypothesis that structural features which predispose to localization of charge at a strongly favored site are not conducive to the low-energy fragmentation of peptide ions via a multiplicity of pathways. Consistent with this proposal, it is demonstrated that the formation of N- or C-terminal pre-charged derivatives is detrimental to the formation of sequence-specific product ions following low-energy collisional activation. Protonation of pre-charged derivatives (yielding doubly charged ions) restores favorable fragmentation properties; the effect is attributed to the fragmentation-directing properties of the proton which may occupy one of several sites.

Influence of cysteine to cysteic acid oxidation on the collision-activated decomposition of protonated peptides: Evidence for intraionic interactions.

Oxidation of cysteine residues to cysteic acids in C-terminal arginine-eontaining peptides (such as those derived by tryptic digestion of proteins) strongly promotes the formation of multiple members of the Y- series of fragment ions following low energy collision-activated decomposition (CAD) of the protonated peptides, Removal of the arginine residue abolishes the effect, which is also attenuated by conversion of the arginine to dimethylpyrim-idylornithine. The data indicate the importance of an intraionic interaction between the cysteic acid and arginine side-chains. Low energy CAD of peptides which include cysteic acid and histidine residues, also provides evidence for intraionic interactions.