Neuropeptide structure elucidation

Mass spectrometry is another detection technique widely used in neuropeptide analysis. Concentration sensitivities in CE-MS do not reach those obtained by CE-LIF nevertheless, tedious derivatization procedures are avoided. In addition, CE-MS has proven to be a powerful tool for structure elucidation as illustrated by the investigation of the in vivo metabolic fate of peptide E by Caprioli s group [12]. After microdialysis and in-line SPE, neuropeptides migrating out of the electrophoresis capillary were deposited directly onto a precoated cellulose target used in matrix-assisted laser desorption-time of flight (MALDI-TOF) MS subsequently. Structural information is then obtained along with the mass of the peptide(s). 

Although HPLC-MS has been applied to many substance of biological interest (e.g., steroids, small peptides) (Games, 1981 Games et ai, 1980), practical considerations have limited its use in neuropeptide studies. Not the least of these problems is the nonuniform fragmentation of underi-vatized peptides under El and Cl modes, which makes structure elucidation extremely difficult, if not impossible. 

The structural analysis of membrane-associated peptides comprises two steps (a) the elucidation of the three-dimensional fold of the peptide and (b) the determination of the membrane-peptide interface. We will use our results gained for the 36 amino acid residue neuropeptide Y (NPY) [83] to demonstrate the approaches that can be used. NPY regulates important pharmacological functions such as blood pressure, food intake or memory retention and hence has been subject of many investigations (for a review see Ref. [84]). It targets the so-called Y receptors that belong to the class of seven transmembrane receptors coupled to G-proteins (GPCRs). 

Raina and Klun, 1984), but it wasn t until 1989 that the structure of the pheromone biosynthesis activating neuropeptide (PBAN) was elucidated (Raina et al., 1989). The rapid advances in this area in the last decade are chronicled by Rafaeli and Jurenka (Chapter 5). 

The elucidation of the primary structures of proctolin (22) and AKH (2Q), signaled the beginning of the structural identification of insect neuropeptides. These relatively small peptides (pentapeptide proctolin and decapeptide AKH) remained the only known insect peptide sequences for a number of years until, in the early 1980 s, accumulated technical advances in peptide isolation and microsequencing techniques facilitated the analysis of insect peptides (8-12 ... 

Schistomyotropins (Scg-MT), neuropeptides from the CNS of the desert locust Schistocerca gregaria). The peptides were isolated from the methanolic extract of about 7000 brains of these insects. The primary structures were elucidated as follows schistomyotropin-1 (Scg-MT-1)... 

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