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.

Did this answer your question?