The fast atom bombardment mass spectra of 24 alpha-amino acids have been studied. These include the mass spectra as well as the metastable ion MI and collisional activation CA spectra of [M + H]+ and [M - H]- ions. The extent of the common neutral losses as NH3, H2O and CO2H2 in the positive ion spectra is governed by the nature of the side chain. The relationship between the fragmentation behaviour of the negative ions and the presence of particular functional groups is less obvious. Mixtures of amino acids in glycerol show pronounced surface effects.

The positive- and negative-ion collision-induced dissociation spectra of peptides containing methionine, methionine sulphoxide and methionine sulphone have been studied. Characteristic fragmentations were identified and evaluated as possible indicators for the presence of oxidized methionine residues in peptides. It was found that the elimination of CH3SOH (-64 u) from [M + H]+ is unique for peptides that contain methionine sulphoxide. Sequence ions containing the oxidized methionine undergo the same elimination, allowing unambiguous sequence determination. Methionine sulphone exhibits an analogous elimination of CH3SO2H (-80 u) from the protonated molecule, but not from sequence ions.

A particularly interesting class of oligomeric peptidomimetics is formed by the peptoids, which consist of N-substituted glycine residues. A solidphase synthesis method for peptoids is presented in which these residues are introduced using their Fmoc derivatives. This ªmonomerº method allowed the monitored synthesis of relatively large quantities of pure peptoids as well as the translation of, in principle, any peptide into the corresponding peptoid. The required Fmoc-substituted glycines were accessible by convenient synthesis, and a number of monomers including those containing side chains with functional groups have been synthesized. The use of Fmoc monomers also allowed implementation of a solid-phase synthesis protocol on a commercial peptide synthesizer. The method was exemplified by the solid-phase syntheses of the (retro)peptoids of Leu-enkephalin and substance P. Mass spectrometric studies of (retro)peptoids were essential for their characterization, and the presence of the B-and Y''-type ions allows sequence analysis. Substance P (retro)-peptoids were biologically active. HPLC analysis showed an increased hydrophobicity, and pepsin treatment resulted in greatly reduced degradation compared with the corresponding peptide.

The protonated and sodium cationized pseudomolecular ions of a series of reducing and non‐reducing oligosaccharides possessing aldopentopyranosyl, 6‐deoxyaldohexopyranosyl, ketohexofuranosyl, 4‐O‐methyl glucuronopyranosyl methyl ester and N‐acetyl 2‐deoxyglucopyranosylamine units were studied using collision‐induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H]+ ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na]+ ions by two‐bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 → 2 and 1 → 4 linkages. The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H]+ and [M + Na]+ ions is discussed. An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H]+ ions and oxonium ions from several oligosaccharides containing monosaccharide residues with different masses.

No abstract

The negative ion mass spectrometric characteristics of a series of di- and trisaccharides and the tetrasaccharide stachyose have been studied using fast atom bombardment mass spectrometry. The molecular weight of the compounds can easily be derived from their mass spectra, which all show an abundant [M - H]- ion peak. The application of metastable ion and collisional activation techniques to selected pseudomolecular and fragment ions appears to be appropriate for the determination of the position and anomeric type of linkage in the molecules, and provides information concerning the monosaccharide units involved. Important fragmentation reactions have been traced and reaction mechanisms, supported by deuterium labelling experiments, are proposed. An experiment describing the application of the findings of this study to a glycosphingolipid molecule demonstrates its potential value for biological systems.

A new adipokinetic hormone (named Lom-AKH-111) was isolated from the glandular lobes of the corpora cardiaca of Locusta migratoria. At the N-terminus it is blocked by a 5-oxoproline (pyroglutamic acid) residue (< Glu). After enzymatic deblocking, the amino acid sequence of the N-terminus was partly established by automatic Edman degradation to be 1 < Glul-Leu-Asn-Phe-Thr-Pro-. Fast-atom-bombardment spectrometry (FAB-MS) revealed that the new hormone is an octapeptide, which is amidated at the C-terminus, and has a relative molecular mass of 1072. Based on the FAB-MS data the complete sequence is < Glu-Leu-Asn-Phe-ThrPro-Trp-Trp-NH,, which was confirmed by chemical synthesis. All characteristics from HPLC, FAB-MS and biological activity of the natural hormone and the synthetic peptide appeared to be identical. Although the structure of this new hormone resembles that of Lom-AKH-I ( < Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH,), its amino acid sequence points to a completely different route for its biosynthesis, involving a third prohormone. High-[K+]-containing media can cause release of all three adipokinetic hormones in vitro. Interestingly, the new hormone is absent in another locust species, Schistocerca gregaria. Based on in vitro biosynthesis experiments the turnover for this hormone is very high, suggesting an important physiological function. Locusta migratoria is the first insect species in which three different adipokinetic hormones have been demonstrated.The first physiological evidence for the presence of compound(s) with adipokinetic activity in the corpora cardiaca (CC) of the locusts Locusta migratoria and Schistocerca gregaria was reported independently by Beenakkers [l] and by Mayer and Candy 121, respectively. From both species an identical adipokinetic hormone (AKH) was isolated (Lom-AKH-I; for nomenclature see [3]) and sequenced ( < Glu-LeuAsn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH,) 141. Both species also contain a second adipokinetic hormone [5] and sequence analysis revealed that this hormone in Locusta (Lom-AKH-11) ( < Glu-Leu-Asn-Phe-Ser-Ala-Gly-Trp-NH,) differs in only one amino acid from that in Schistocerca (Scg-AKH-11) ( < Glu-Leu-Asn-Phe-Ser-Thr-Gly-Trp-NH2) [6].AKHs are synthesized and stored in the glandular lobe of the CC [7 -91 and are colocalized in the same secretory granCorrespondence to R.

The phenomenon of 'internal residue loss' of protonated native- and per-O-methylated oligosaccharides has recently been described as occurring on high-energy collision conditions. Awareness of this phenomenon in the mass spectrometric analysis of oligosaccharides is of great importance since the rearrangement ions produced by this process may complicate monosaccharide sequence assignment. In this research, oligosaccharides having N-acetyl-glucosamine residues as the reducing or non-reducing terminal residue have been included in our MS/MS analyses in order to try to better understand the factors that influence 'internal residue loss'. Native and per-O-methylated compounds were submitted to positive and negative MS/MS, selecting protonated, sodium-cationized, or de-protonated pseudomolecular ions as precursors. High- and low-energy collision induced dissociation tandem mass spectrometry experiments were performed using a four sector instrument and a hybrid quadrupole time-of-flight mass spectrometer respectively. The phenomenon of 'internal residue loss' was not observed on either high- or low-energy CID-MS/MS when sodium-cationized precursor ions of either native or per-O-methylated oligosaccharides were examined. Similarly, MS/MS analysis performed in the negative ionization mode also failed to generate ions resulting from 'internal residue loss'. This combination of experiments therefore offers a way to be sure whether ions observed in the tandem mass spectra of protonated native or per-O-methylated oligosaccharides originate from 'internal residue loss' or from direct glycosidic linkage fragmentation.