Calculation of protein molar extinction coefficient (ɛ) with values from Pace et al. 1995

Abstract

Calculation of molar extinction coefficient (ɛ) at 280 nm based on amino acid sequences and the estimated contribution from tyrosine, tryptophan and cystine residues. The contributions of the residues in guanidine hydrochloride are based on measurements performed on free amino acids in solvent. The contributions of the residues in water are the averages from the analysis of 80 proteins.

Instructions

1	Count the number of tryptophans, tyrosines and cystines (cysteine residues in disulfide bonds - not reduced residues)
2	For 6 M Guanidine Hydrochloride, use the formula ɛ₂₈₀ = (No. of tryptophan residues)(5,685) + (No. of tyrosine residues)(1,285) + (No. of cystines)*(125)
3	For water, use the formula ɛ₂₈₀ = (No. of tryptophan residues)(5,500) + (No. of tyrosine residues)(1,490) + (No. of cystines)*(125)
4	For 8 M Urea, use the formula ɛ₂₈₀ = (No. of tryptophan residues)(5,630) + (No. of tyrosine residues)(1,300) + (No. of cystines)*(115)

Reference(s)

Reference	Title	PMID/ISBN
Pace et al. 1995	How to measure and predict the molar absorption coefficient of a protein	8563639

1	Count the number of tryptophans, tyrosines and cystines (cysteine residues in disulfide bonds - not reduced residues)
2	For 6 M Guanidine Hydrochloride, use the formula ɛ₂₈₀ = (No. of tryptophan residues)(5,685) + (No. of tyrosine residues)(1,285) + (No. of cystines)*(125)
3	For water, use the formula ɛ₂₈₀ = (No. of tryptophan residues)(5,500) + (No. of tyrosine residues)(1,490) + (No. of cystines)*(125)
4	For 8 M Urea, use the formula ɛ₂₈₀ = (No. of tryptophan residues)(5,630) + (No. of tyrosine residues)(1,300) + (No. of cystines)*(115)