BETA-ENDORPHIN-CONTAINING PROTEINS IN THE HUMAN PITUITARY

Two new proopiomelanocortin (POMC)-derived beta-endorphin (BE)-contain ing proteins were detected in the human pituitary, using HPLC, trypsin digestion, and a high sensitivity search with liquid secondary ion ma ss spectrometry (LSIMS) for the protonated molecule ion, (M+H)(+), of tryptic peptides that are unique to BE. Proteins were extracted from p ituitary tissues and were purified by solid phase extraction (SPE) chr omatography and RP-HPLC. Each HPLC fraction was treated with trypsin, and each unseparated peptide mixture was analyzed by LSIMS to detect t he two selected marker peptides (BE20-24 and BE10-19) that have excell ent LSIMS desorption-ionization properties. The detection of both of t hose peptides indicated the presence of BE-containing proteins in two HPLC fractions (number 47 and 51). Tandem MS determined the amino acid sequence of the marker peptide BE20-24 (NAIIK), and those sequence da ta optimized the specificity of the method. The two new BE-containing proteins derive from the C-terminal region of POMC, and were minor com ponents in the two HPLC fractions. The major component in fraction 51 derived from the vasopressin-neurophysin 2-copeptin precursor. (C) 199 7 Elsevier Science Inc.