The molecular weight of a protein is calculated by adding up the molecular weights of the amino acids, per standard calculations.

In Benchling, the following molecular weights are assigned to amino acids:

  • A: 89.09 
  • B: 132.65
  • C: 121.15
  • D: 133.1
  • E: 147.13
  • F: 165.19
  • G: 75.07
  • H: 155.16
  • I: 131.17
  • J: 131.2
  • K: 146.19
  • L: 131.17 
  • M: 149.21
  • N: 132.12
  • O: 255.31
  • P: 115.13
  • Q: 146.15
  • R: 174.2
  • S: 105.09
  • T: 119.12
  • U: 168.06
  • V: 117.15
  • W: 204.23
  • X: 143.7
  • Y: 181.19
  • Z: 146.75

Notes

We have lightly modified constants from biopython, to match results from expasy. These are the average isotopic masses, as opposed to the monoisotopic mass. See http://www.ionsource.com/tutorial/isotopes/slide8.htm.

Molecular weights for B and Z are non-standard and were reverse engineered from
http://web.expasy.org/protparam/.

Molecular weights for J and X were taken from Geneious.

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