Figure 2.3 Ultraviolet absorption spectra of the aromatic amino acids and bovine serum albumin.
(A) Aromatic amino acids such as tryptophan, tyrosine, and phenylalanine have absorbance maxima at ∼280 nm. Each purified protein has a distinct molecular absorption coefficient at around 280 nm, depending on its content of aromatic amino acids.
(B) A bovine serum albumin solution (1 mg dissolved in 1 ml of water) has an absorbance of 0.67 at 280 nm using a 1 cm cuvette. The absorption coefficient of proteins is often expressed as E1% (10 mg/ml solution). For albumin, E1%280 mm = 6.7. Although proteins vary in their Trp, Tyr, and Phe content, measurements of absorbance at 280 nm are useful for estimating protein concentration in solutions. |
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| Aspartic and glutamic acids contain carboxylic acids on their side chains and are ionized at pH 7.0, and, as a result, carry
negative charges on their β- and γ-carboxyl groups, respectively. In the ionized state, these amino acids are referred to as aspartate and glutamate, respectively.
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