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Determination of peptide sequence via MSn |
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| To confirm known peptide sequences the method of MSn is used. After electrospray ionization (ESI) of the peptide collision induced fragmentation (CIF) leads to a couple of different kind of peptide fragments: | |
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| Fragments will only be detected if they carry at least one charge. If this charge is retained on the N terminal fragment, the ion is classed as either a, b or c. If the charge is retained on the C terminal, the ion type is either x, y or z. An index indicates the number of residues in the fragment. In addition to the proton(s) carrying the charge, c ions and y ions abstract an additional proton from the precursor peptide. These structures include a single charge carrying proton. In electrospray ionisation generally basic peptides carry two or more charges, so those fragments may carry more than one proton. Double backbone cleavage gives rise to internal fragments. Usually, these are formed by a combination of b type and y type cleavage, an amino acylium ion. Sometimes, internal ions can be formed by a combination of a type and y type cleavage, an amino-immonium ion. An internal fragment with just a single side chain formed by a combination of a type and y type cleavage is called immonium ion. | |
| With the information of the different fragment masses the sequence of a peptide can be determined. Whether the complete sequence is to verify depends on the length of the peptide and on the sequence. Usually peptides up to 20-30 amino acids can be verified completely. Extreme stable pair of amino acids might lead to gaps in sequence covering. | |
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| Results: molecular weight y, b and a-type fragments which are to determine. Peptide sequence, that is determined What we need: |
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