Measurement of protein by spectrophotometry at 205 nm

A method is described for the measurement of protein concentration by using the peptide bond absorption at 205 nm. ?₂₀₅ is estimated, allowing for the absorption due to Trp and Tyr residues, by measuring the absorbance at 280 nm as well as at 205 nm. The estimated ?₂₀₅ is compared with the actual ?₂₀₅ for a number of proteins, the mean error being less than 2%. This is about three times better than using an average ?₂₀₅^{1 mg/ml} of 31 and approaches the range of experimental error inherent in any method of protein estimation.