Notes on...

Calculating the extinction coefficient

The molar extinction coefficient e at 280 nm of a peptide can be estimated by calculating

The equation for the extinction coefficient of a peptide.

where nW, nY, and nC are the number of Tryptophans (W), Tyrosines (Y) and Cystines (i.e. disulphide bonds, but here denoted C) in the sequence. The molar extinction coefficients used in Innovagen's Peptide Calculator are:

eW = 5690 M-1cm-1 eY = 1280 M-1cm-1 eC = 120 M-1cm-1  
Gill and von Hippel

Note: Your peptide may contain non-natural amino acids, modifications and labels. None of these are considered, although they may very well add to the extinction coefficient.

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