OMS Letters
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MASS SPECTRAL ANALYSIS OF SULFATED LEUCINE ENKEPHALIN USING FAST ATOM BOMBARDMENT AND LINKED-FIELD SCAN TECHNIQUES
Although sulfate esters of certain neuropeptides have been detected in body tissues,' the exact biological significance of this post-translational modification is yet to be understood completely. To gain insight of the functional role of the sulfate conjugation, it is imperative to define accurately its location and to determine the amino acid sequence of the modified neuropeptide.
In an effort to develop a mass spectrometry (MS) method for analysis of sulfated neuropeptides, a preliminary study was undertaken to characterize Tyr-Osulfated leucine enkephalin (LE-SOq). Magnetscan and B/€ linked-field scan in the positive-and negative-fast atom bombardment (FAB) ionization modes were both used to obtain knowledge of the fragmentation behavior of LE-SO4. With this knowledge, it is possible to deduce the amino acid sequence of the peptide. Leucine enkephalin (YGGFL =LE), an important opioid-active peptide, is synthesized in the brain and adrenal medulla in the form of two large precursor proteins, proenkephalin A and proenkephalin B.2 Its sulfated form has also been detected in sheep, mouse, and guinea pig striaturn both as free LE-SO4 and as incorporated in precursor p r ~t e i n . ~ A VG 7070E-HF double-focusing forward-geometry mass spectrometer and DEC PDP 11/24based VG 11 -250M+ data system was used to obtain magnet-scan and B/€-collision-activated dissociation (CAD) mass spectra. FAB employed an Ion Tech B11 NF saddle-field gun to generate an ionizing beam of Xe atoms of ca. 7 keV energy and 1 mA beam flux. The FAB-desorbed ions exited the ion source at 6 kV potential. Helium was used as a collision gas and glycerol as a FAB matrii.