Calculateur Beer-Lambert pour Protéines
Calculez la concentration protéique par la loi de Beer-Lambert.
Estimated Molecular Weight
33,018 Da
Estimated Molecular Weight vs Number of Amino Acid Residues
Formule
## Protein Molecular Weight Estimation The molecular weight of a protein can be estimated from the number of amino acid residues using the average residue weight. ### Formula **MW = N × 110 + 18** where N is the number of residues and 110 Da is the average amino acid residue weight (after peptide bond formation removes water). The +18 accounts for the water molecule completing the N-terminus and C-terminus. The actual average residue weight is 111.1 Da for a typical protein composition.
Exemple Résolu
A protein with 300 amino acid residues.
- 01MW = 300 × 110 + 18 = 33,018 Da
- 02MW = 33.0 kDa
Questions Fréquentes
How accurate is this estimate?
Within about 5-10% for most proteins. Actual MW depends on the amino acid composition. Proteins enriched in heavy amino acids (Trp, Tyr) will be heavier, while glycine-rich proteins will be lighter.
What about post-translational modifications?
Glycosylation can add 2-50 kDa or more. Phosphorylation adds ~80 Da per site. Disulfide bonds subtract 2 Da per bond. Prosthetic groups (heme, FAD) add their own mass.
How is protein MW measured precisely?
Mass spectrometry (MALDI-TOF or ESI) gives accuracy within a few Daltons. SDS-PAGE gives estimates within 10-20%. Size exclusion chromatography can give rough estimates for native proteins.
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