W. Heerma

Loss of internal 1 → 6 substituted monosaccharide residues from underivatized and Per-O-methylated trisaccharides

The fragmentation behavior of [M + H]+ ions of a series of underivatized and per-O-methylated trisaccharides having 1 → 6 linked residues, of which one or two is a deoxy-fluoro or deoxy residue and thus has a unique mass, has been studied by using collision-induced dissociation fast-atom bombardment mass spectrometry. In addition to the usual fragment ions resulting from glycosidic bond cleavage, fragment ions were observed which must have been generated following an unusual rearrangement process which can be rationalized in terms of the loss of an internal monosaccharide residue.

Structure identification of natural rhamnolipid mixtures by fast atom bombardment tandem mass spectrometry

Two rhamnobiose-lipid preparations have been studied by fast atom bombardment (FAB) tandem mass spectrometry. The principal rhanobiose-lipids contain the β-hydroxydecanoyl-β-hydroxydecanoate Rha-Rha-C10-C10 and the β-hydroxytetradecanoyl-β-hydroxytetradecanoate Rha-Rha-C14-C14. Both preparations contain minor components which are heterogenous in β-hydroxy fatty acid composition. FAB ionization of rhamnobiose-lipids in the presence of Na+ shows the formation of both [M + Na]+, [M + 2Na - H]+, [M + 3Na - 2H]+ and [M - H]− ions. Tandem mass spectrometry of the [M + 2Na - H]+ and [M - H]− ions give information about the sequence of the building blocks. Particularly, heterogeneity in β-hydroxy fatty acid composition is determined for the principal components and all the minor components present in the preparations.

Comparison between collision induced dissociation of electrosprayed protonated peptides in the up-front source region and in a low-energy collision cell

A systematic comparison between the up-front Collision induced dissociation (CID) mass spectra and low-energy CID tandem mass spectra from twenty-one singly and/or doubly charged peptides has been made. CID spectra of the peptides were recorded at different electrode voltages in the up-front source region of a single quadrupole instrument and different collision energies in the collision cell of a tandem quadrupole instrument. It was observed that up-front CID and low-energy CID yielded comparable product ion spectra from protonated peptides, and that the instrumental settings necessary for obtaining comparable CID mass spectra from the two methods are correlated.

The B1-fragment Ion from Protonated Glycine is an Electrostatically-bound Ion/Molecule Complex of CH2=NH+2 and CO

The stability of the B1-ion from glycylglycine dipeptides was studied using collision-induced dissociation experiments and ab initio calculations. This study reveals that the B1-type ion from glycine should be considered as an electrostatically bound ion/moecule complex, which dissociates into a glycine immonium ion (A1) and a carbon monoxide molecule. The stability of this complex has been calculated at various levels of the theory. At the highest level of theory (#RHF/6-311G**) it is found that the energy requirement, including zero-point vibrational energy correction, for dissociation into a glycine immonium A1 ion and a neutral carbon monoxide CO molecule is −4.0 kJ mol−1. Furthermore it could be concluded that B1-ions from glycine are stable if they are present as N-acylated species. The formation of stable B ions requires at least two carbonyl groups in the peptide backbone moiety.

Action of a cell-envelope proteinase (CEPIII-type) from Lactococcus lactis subsp. cremoris AM1 on bovine κ-casein

The specificity of the cell-envelope proteinase (CEPIII-type) from Lactococcus lactis subsp. cremoris AM1 in its action on bovine κ-casein was studied. A 4-h digest (pH 6.2, 15°C) of κ-casein was made with the purified proteinase. The pH-4.6 soluble fraction, representing more than 95% of the whole hydrolysate, was ultrafiltered to obtain a high-molecular-mass (HMM) and a low-molecular-mass (LMM) fraction, which were separately further purified by electrophoretic and chromatographic techniques. Isolated HMM and LMM products were identified by amino acid analysis, end-group determination and mass spectrometry. On-line HPLC/mass spectrometry was also used for the separation of an LMM peptide mixture and the identification of its components. The HMM products formed were the fragments 1–160, 1–151, 1–95 and 1–79 of κ-casein, whereas the main LMM products found were the 161–169 and 152–160 fragments. The enzyme specificity was concluded to be primarily directed towards the C-terminal region of the substrate molecule by cleavage of the 160–161 and 151–152 peptide bonds. Two minor LMM products were identified as the fragments 96–104 and 103–106, indicating additional cleavage at positions 102–103, 104–105 and 106–107 of the sequence. Also several peptide bonds within the 161–169 sequence were found to be subject to secondary cleavage by the proteinase. From electrophoretic and identification data it is concluded that the lactococaal CEPI, CEPIII and several mixed-type proteinases all act on the peptide bonds at positions 79–80 and 95–96. However, the C-terminal region of the κ-casein sequence is the exclusive target of the CEPIII-aand, to variable extents, of the mixed-type enzymes.

Rapid analysis of enzymatic digests of a bacterial protease of the subtilisin type and a “bio-engineered” variant by high-performance liquid chromatography—frit fast atom bombardment mass spectrometry

Amino acid sequencing of a subtilisin-type bacterial protease and a bio-engineered variant was carried out by investigating various enzymatic digests using HPLC-frit fast atom bombardment MS methods. The fast atom bombardment mass spectral data allowed rapid identification of the enzymatically generated peptides and differentiation between both proteins. The feasibility of determining the positions and nature of mutations in the amino acid sequence depends mainly on the size of the peptides containing the modifications.

Electron-impact induced fragmentation of some hetero- cyclic-tin compounds

The electron impact induced fragmentation of a series of heterocyclic tin compounds: 10,10-dimethyl- and 10,10-diethylphenoxastannim, the corresponding dimethyl- and diethyltin twelve membered ring heterocycles. 10-10- dimethylphenothiastannin, 10,10-dimethylphenothiastannin 5,5-dioxide, 5,5-dimethyl -5,10-dihydrodibenzo [b,e]stannin and 10,10′ -spirobiphenoxastannin, has been investigated. For the twelve membered ring compounds the results strongly support the structures given by Meinema and Noltes [2]. Primary fragmentation occurs by loss of an alkyl group, in accordance with the preferred tervalency of the tin ion. Further fragmentation pathways were established in each case by defocused metastable measurements and exact mass measurements. Loss of Sn-containing fragments is more common than in Sn- tetraalkyls because of charge stabilisation on the aromatic system. Large differences were observed in molecular ion intensities of the various compounds investigated. Their intensities could be correlated with ionization potentials of the aromatic substituent. A theory attributing this to charge residence in put forward.

Electron-impact mass spectrometry of methyl 2,3,5,6-tetra-O-methyl-d-glucofuranoside

Abstract The fragmentation of methyl 2,3,5,6-tetra- O -methyl- d -glucofuranoside under electron impact is described using data for labelled analogues and metastable measurements. Although the fragmentation showed features of that of hexopyranosides and pentofuranosides, there were characteristic differences. Mass-spectral data that are useful for identification of pentoses and hexoses as pyranosides or furanosides are tabulated.

S9.16 Determination of linkage positions by FAB-mass spectrometry

Recently, FAB was used for linkage position determination of intact oligosaccharides, using the negative ion mode for underivatized samples and the positive ion mode (collisionactivated decompositions) for derivatized samples. We report linkage analysis of (methyl) peracetylated xylo-oligosaccharides by FAB, using the positive ion mode and unimolecular decompositions in the 3 r~ FFR of a four sector instrument (JMS-SX/SX102A; BEBE). The MS/MS spectra of the m / z 475 oxonium ions of the disaccharides (1~2, 1~3 and 1~4) are very different. Distinction of the linkage type can be based on the presence or absence of certain fragment ions (see table). All spectra show peaks at m / z 415 and m / z 259 (loss of acetic acid and cleavage of the glycosidic bond, resp.). The spectra of the 1~2 compounds show an additional peak at m / z 355 (loss of a second molecule of acetic acid), which is absent in the other spectra, and a low intensity peak at m / z 199 (formed by loss of acetic acid from the m / z 259 ion). The spectra of the 1~3 compounds show a peak at m / z 373 (loss of C4H603) and an abundant peak at m / z 199, formed mainly by elimination of a complete saccharide, consisting of the ring at the non-reducing end, the oxygen of the glycosidic bond and a hydrogen atom, transferred from the other ring. The MS/MS spectra of m / z 475 of the peracetylated tri-, tetraand pentasaccharides (Xyl ( l~n)Xyl ( l~4)Xyl (n: 2, 3 or 4), Xyl4 and Xyl5 only 1~4) show identical fragment ions as their corresponding disaccharides. The MS/MS spectra of oxonium ions with higher masses (three, four and five ring systems, resp.), all show only loss of one molecule of acetic acid and cleavage of the glycosidic bonds, confirming a 1~4 linkage between the two rings at the reducing end.