Dear Skyline team,

thank you for providing us with the possibility to get numbers representing protein abundance per replicate directly from Skyline, which is also supposed to be part of the next main Skyline release. I intend to use this option rather frequently in my research and would like to understand it a bit better. I am mainly interested in the normalization case against heavy (each light signal must have a heavy counterpart to be considered).

In the release notes, you state that this protein abundance value is the same that the Group Comparison (GC) framework uses. I thought that, as default, on protein level GC sums up all transition areas that belong to the same protein (also across different peptides) that are quantitative and have a heavy counterpart and then normalizes this sum to the sum of heavy signals. This is slightly different compared with calculating normalized ratios transition by transition and then averaging those ratios, since strong signals dominate the sums of values, as previously described on several occasions. However, the explanation in the reporting window for the "Protein Abundance" feature now states that "The Protein Abundance is calculated by taking the average of the normalized areas of all of the Transitions under the Protein." This now sounds to me exactly as the latter option to do it and the question is, whether protein abundance numbers really are exactly what the GC framework uses?

Thanks a lot,

Roman