Rapid and efficient sequence determination of a 4 nmol sample of adipokinetic hormone I (AKH I) using FAB tandem mass spectrometry

Primary sequence analysis by fast atom bombardment mass spectrometry of a peptide with adipokinetic activity from the corpora cardiaca of the cricket Gryllus bimaculatus

The octapeptide AKH-G, isolated from the cricket Gryllus bimaculatus, stimulates lipid mobilization in both the cricket itself and in migratory locusts. The structure of AKH-G has been assigned by fast atom bombardment mass spectrometry (FABMS) as pGlu-Val-Asn-Phe-Ser-Thr-Gly-Trp-NH2, and it is most closely related to AKH II-S from Schistocerca species, which has a Leu2 unit. Synthetic AKH-G, prepared by solid phase techniques, had the same bioactivity as the natural substance. FABMS measurements, including high-resolution and metastable studies, were made employing 400-900 pmole of sample.

Unequivocal structure assignment of C- versus N-alkylated amino acids using fast atom bombardment/tandem mass spectrometry

Structure assignment of the isomeric immonium ions 5 and 6, generated via FAB from N-isobutyl glycine and N-methyl valine, can be achieved by their collision induced dissociation characteristics.

Sequence determination of N-terminal and C-terminal blocked peptides containing N-alkylated amino acids and structure determination of these amino acid constituents by using fast-atom-bombardment/tandem mass spectrometry

Peptides, blocked either at the N or C terminus, and thus unsuited for Edman degradation, and those containing N-alkylated amino acids, which are not detectable when using conventional amino acid analysis, can be easily sequenced by applying a method in which fast atom bombardment (FAB) is combined with tandem mass spectrometry (MSMS). Moreover, the structure of the N-alkylated amino acid constituents is provided by this approach. A widely applicable strategy will be presented, and to demonstrate its scope and limitations eighteen analogues of sequences related to the C terminus of substance P, a biologically active neuropeptide, were investigated. The power and reliability of the approach will be demonstrated by analyzing an 'unknown' peptide. Moreover, the detection and structure elucidation of N-alkylated amino acids which usually escape amino acid analysis will be described, as will be the unequivocal differentiation and identification of isomeric MeLeu/MeIle. The influence of the N-alkylation on the mass spectrometric fragmentation behaviour will be discussed. Furthermore, the sequencing of two adipokinetic hormones by using the combined FAB-MSMS approach is described. Analysis of peptides can be achieved with sample sizes less than 0.1 mumol and be completed within 2-4 h.