What you are given
- Amino-acid sequence: MKWVTFISLLFLFSSAYSWWYY
Formula: ε280 = nW·5500 + nY·1490 + nSS·125
Spectrophotometry
How do you calculate protein extinction coefficient (A280)?
Sequence to ε280, MW, and E0.1%, the Pace way. Feeds the A280 calculator. The relationship used is ε280 = nW·5500 + nY·1490 + nSS·125.
Worked example
Every number below is computed by the calculator, not typed in
The working
- Composition:
22 residues; Trp 3, Tyr 3, Cys 0 - ε280:
3·5500 + 3·1490=20970 M⁻¹cm⁻¹ - MW:
Σ residue masses + 18.01528=2839.35 g/mol - E0.1% (A280 of 1 g/L):
ε / MW=7.386
ε₂₈₀ = 20970 M⁻¹cm⁻¹.
Do it with your own numbers.
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