METABOLISM OF BETA-ENDORPHIN IN PLASMA STUDIED BY LIQUID-CHROMATOGRAPHY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Degradation of synthetic human beta-endorphin by a human plasma protei nase was studied with high-performance liquid chromatography in combin ation with mass spectrometry. The peptide was metabolized at a rate of 25 pmol/min to the major fragments beta-endorphin (1-19) and (20-31), the latter reported as a potent inhibitor of morphine-and beta-endorp hin-induced analgesia in mice. The proteinase responsible for this pro cess was classified as a metal-dependent serine proteinase and was eff ectively inactivated by phenylmethylsulfonyl fluoride and ethylenediam inetetraacetic acid. Identification of the products formed during the enzymatic reaction was performed by liquid chromatography on-line with electrospray mass spectrometry, using a reversed-phase or a novel siz e-exclusion column capable of separating molecules between 0.1-7 kilod altons. Peptide sequences were verified by tandem mass spectrometry ex periments. The conversion of beta-endorphin may have physiological imp lications in the mechanism of pain. The obtained data suggest that sev eral precautions should be considered during recovery and measurement of beta-endorphin in plasma by immunological techniques. The applied s trategy may also be useful for studying metabolism of various peptider gic compounds with potential pharmacological significance. (C) 1998 El sevier Science B.V.