MATLAB: Molweight function gives wrong values

maker

Im trying to get the sum of molecular weights of an amino acid string, lets say, 'MKSHFATYQRV'. When I get molecular weights of individual amino acids it gives exact values. But when I apply molweight function to string of amino acids it gives a difference of 18 points. Please help me resolve it. TIA.

Best Answer

I do not have the Bioinformatics Toolbox, so I cannot check this.
The function may assume that a string of amino acids are a peptide, the individual amino acids being covalently bonded to each other. Peptide bonds each involve a dehydration reaction, so there are likely fewer atoms in the peptide than in the individual amino acids. You can probably use the atomiccomp (link) function to check this.
The molecular weight of water is about 18, and there are 11 amino acids in your peptide, creating 10 peptide bonds, so while I cannot determine what you intend by ‘points’, the difference is likely 180 g/mole.
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