STRUCTURAL MEASUREMENTS ON SEVERAL ALAMETHICIN PEPTIDES BY THE TIME-OF-FLIGHT CORRELATION TECHNIQUE

Time-of-flight correlation methods have been used to determine the pri mary structure of the major component in a nonstandard preparation of alamethicins, and to give some sequence information about minor compon ents. The peptide (MW approximate to 2000 u) is blocked at the N termi nus with an acetyl group and has a primary alcohol rather than a carbo xyl group at the C terminus, so the usual wet chemical sequencing meth ods cannot be applied. Upon bombardment with 25 keV I- ions, the pepti de, deposited on the surface of a solid target, produces both molecula r ions and prompt fragment ions (i.e. ions formed at or very near the surface of the target). After acceleration, these ions may undergo met astable decay as they pass along the flight tube of a reflecting time- of-flight mass spectrometer. Measurement of the correlations between t he neutral and charged daughters from these decompositions determines the decay pattern of each ion, which in turn yields definitive informa tion about the sequence of the original peptide. All events are record ed on magnetic tape and analyzed off-line, so a single run on the spec trometer provides information on the decay of every ion produced at th e target, i.e. information similar to that obtainable from a complete set of daughter ion scans on a multiple sector or triple quadrupole in strument.