Identification of synaptic metabolites of dynorphin A (1-8) by electrospray ionization and tandem mass spectrometry.

Synaptic metabolism of the endogenous opioid octapeptide dynorphin (Dyn) A (1-8) (Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile) was studied in vitro upon its incubation with synaptosomes and with synaptosomal plasma membranes isolated from rat brain tissue. Electrospray ionization (ESI) and tandem mass spectromety were performed using an ion trap instrument, and afforded the identification of Dyn A (2-8), Dyn A (1-6) and leucine enkephalin [Dyn A (1-5)] as major metabolites. Preliminary quantitative data on the kinetics of Dyn A (1-8) degradation and metabolite formation was obtained by size-exclusion chromatography/ESI tandem mass spectrometry, and revealed an apparent involvement of several enzymes in the metabolism upon incubation with synaptosomes. Predominant formation of Dyn A (1-6) was observed with the synaptosomal plasma membranes.