IDENTIFICATION OF POMC PROCESSING PRODUCTS IN SINGLE MELANOTROPE CELLS BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION-MASS-SPECTROMETRY

The use of matrix-assisted laser desorption/ionization mass spectromet ry (MALDI-MS) in identifying proopiomelanocortin (POMC) processing pro ducts in melanotrope cells of the pituitary intermediate lobe of Xenop us laevis was explored. Mass spectra were obtained with such a high se nsitivity of detection that the peptides could be identified in a sing le melanotrope cell. In addition to known POMC processing products of the Xenopus melanotrope cell, the presence of previously unidentified POMC-derived peptides was demonstrated. Together these POMC processing products accounted for the entire length of the POMC precursor. Furth ermore, Xenopus possesses two genes for POMC and the sensitivity and a ccuracy of the MALDI-MS technique allowed identification of processing products of both the POMC, and POMC, gene. In addition, differences w ere obtained between the mass spectra of melanotrope cells from Xenopu s laevis adapted to different conditions of background illumination. T hese results show that MALDI-MS is a valuable tool in the study of the expression of peptides in single (neuroendocrine) cells.