Hydrogen rearrangement to and from radical z fragments in electron capture dissociation of peptides.

摘要: Hydrogen rearrangement is an important process in radical chemistry. A high degree of H· to and from z· ionic fragments (combined occurrence frequency 47% compared with that z·) confirmed analysis 15,000 tandem mass spectra tryptic peptides obtained electron capture dissociation (ECD), including previously unreported double losses. Consistent the character abstraction, residue determining formation rate z′=z·+H· species found be N-terminal species. The size complementary c′m fragment turned out another factor, z′ dominating over ions for m ≤ 6. atom was abstracted side chains as well α-carbon groups residues composing c′ species, Gln His promoting donation Asp Ala opposing it. Ab initio calculations energies ·A radicals (A amino acid) main driving force abstraction by exothermicity. No valid correlation between N-Cα bond strength this cleavage, indicating other factors than thermochemistry are responsible directing site ECD cleavage. Understanding hydrogen attachment loss should facilitate automatic interpretation protein identification characterization, de novo sequencing.