ENHANCEMENT OF CHARGE-REMOTE FRAGMENTATION IN PROTONATED PEPTIDES BY HIGH-ENERGY CID MALDI-TOF-MS USING COLD MATRICES

Delayed extraction matrix-assisted laser desorption ionisation time-of -flight mass spectrometry (DE-MALDI-TOF-MS) is employed to evaluate it s potential for peptide sequencing using both post-source decay (PSD) and high-energy collision-induced dissociation (CID). This work provid es evidence that complete amino-acid sequences may be obtained employi ng a dual approach including PSD of [M + H](+) ions using a ''hot'' ma trix (alpha-cyano-4-hydroxycinnamic acid, CHCA), followed by high-ener gy CID using ''cold'' matrices (2,5-dihydroxybenzoic acid, DHB; 2,6-di hydroxyacetophenone/di-ammonium hydrogen citrate, DHAP/DAHC). This str ategy ensures that PSD results in a rich variety of product ions deriv ed from charge-driven processes that provide gross structural informat ion. High-energy CID (20 keV collision energy range) of low internal e nergy [M + H](+) ions is then employed to reveal complementary side-ch ain detail (i.e. Leu/Ile distinction) in a manner highly selective for charge remote fragmentation (CRF), because PSD is largely reduced. As expected from the known behaviour of protonated peptides at 10 keV co llision energies, charge fixation at basic sites required for CRF is m ore pronounced in CID than in PSD. We have obtained spectra for a synt hetic peptide that approximate the results and performance of MALDI hi gh-energy CID obtained on sector-based instrumentation (EBE-oa-TOF). ( C) 1997 Elsevier Science B.V.