Formation of N-pyroglutamyl peptides from N-Glu and N-Gln precursors in Aplysia neurons

Matrix-assisted laser desorption/ionization with time-of-flight mass spectr ometry is used to examine the formation of N-pyroglutamate (pGlu) in single , identified neurons from Aplysia. Six pGlu peptides are identified in the R3-14 and the R15 neurons that result from in vivo processing of peptides c ontaining either Glu or Gin at their respective N-termini. Moreover, we sho w that Glu-derived pGlu is not a sample collection or measurement artifact. The pGlu peptides are detected in isolated cell bodies, regenerated neurit es in culture, interganglionic connective nerves, cell homogenates, and col lected releasates. We also demonstrate that R3-14 cells readily convert a s ynthetic N-Glu peptide to its pGlu analogue, indicating the presence of nov el enzymatic activity.