PSI-MOD is an ontology consisting of terms that describe protein chemical modifications
John S. Garavelli
Annotation note 9 - The Open Mass Spectrometry Search Algorithm, OMSSA, enumerated list of modifications are being incorporated. The string values are synonyms with the synonymtypedef "OMSSA-label", and their integer values (which are supposed to be stable) are definition cross-references.
Annotation note 4 - The elemental formulas are in strict alphabetical order, not in CAS ("C" and "H" first) order. Isotope numbers are in parentheses before the element symbol, and an element should not occur in a formula both with and without an isotope number. In difference formulas, counts can be zero or negative.
RESID release: 75.00
ISO-8601 date: 2014-01-28 14:22Z
PSI-MOD version: 1.013.0
Annotation note 2 - When an entry in the RESID Database is annotated with different sources because the same modification can arise from different encoded amino acids, then the PSI-MOD definition for each different source instance carries the RESID cross-reference followed by a hash symbol "#" and a 3 or 4 character label. When an entry in the RESID Database is annotated as a general modification with the same enzymatic activity producing different chemical structures depending on natural variation in the nonproteinaceous substrate, on secondary modifications that do not change the nature of the primary modification, or on a combination of a primary and one or more secondary modifications on the same residue, then the PSI-MOD definition for each different instance carries the RESID cross-reference followed by the special tag "#var".
Annotation note 1 - "[PSI-MOD:ref]" has been replaced by PubMed:18688235.
Annotation note 3 - When an entry in the UniMod database is annotated as a general modification, and one or more instance sites are listed, then the PSI-MOD definition for each different site instance carries the UniMod cross-reference followed by a hash symbol and an amino acid code, "N-term" or "C-term".
Annotation note 7 - The synonym cross-reference "MOD:old name" has been replaced by "MOD:alternate name".
Annotation note 6 - For cross-link modifications, the number following "Cross-link" in the comment record indicates the number of amino acid residues that appear in the origin record, used to check the difference formula and masses. This usage differs from RESID, where the cross-link number indicates the maximum number of peptide chains that can be cross-linked.
Annotation note 5 - In entries with an isotope indicator in the formula, average masses are meaningless and are assigned the value equal to the monoisotopic mass, but rounded to a lower precision; monoisotopic masses are calculated by using the masses for the indicated isotopes and the most common isotopes for other elements without isotope indicators in the formulas.
Annotation note 8 - The DeltaMass listings for free amino acids have been removed. Most UniMod entries that have not been "approved" have by general agreement not been incorporated unless there has been a request for a specific term by a PRIDE submitter.