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How does the LipidBlast plugin handle indistinguishable isomers?

When performing a search using the LipidBlast plug-in, you may encounter search results that differ only in the location and/or geometry of their double bonds.

For example, you may perform a search and find two search results:

  • GPCho(16:0/20:3(8Z,11Z,14Z))
  • GPCho(16:0/20:3(5Z,8Z,11Z))

These two Lipids differ only in the location of the double bonds. We cannot decide which of these search results is correct by looking at mass, formula, or fragmentation pattern. To handle this ambiguity, the LipidBlast plugin provides an option called Report isomers as a single search hit.

When enabled, this option will merge any search results that differ only in double bond location and/or geometry, and report a single hit with no double bond information. In the example given, with Report isomers as a single search hit enabled, the LipidBlast plugin would report a single search result:

  • GPCho(16:0/20:3)

Note that this option does not group isomers whose side chains are different lengths or have different numbers of double bonds. For example, given the following 3 search results:

  • GPCho(16:0/20:3(8Z,11Z,14Z))
  • GPCho(16:0/20:3(5Z,8Z,11Z))
  • GPCho(16:1(7Z)/20:2(11Z,14Z))

With Report isomers as a single search hit enabled, these would be reported as two hits:

  • GPCho(16:0/20:3)
  • GPCho(16:1/20:2)

Although GPCho(16:0/20:3(8Z,11Z,14Z)) and GPCho(16:1(7Z)/20:2(11Z,14Z)) are isomers, they are not merged, as their side chains have different numbers of double bonds.

See also