BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Tyrosine and tryptophan absorb more than do phenylalanine; tryptophan is responsible for most of the absorbance of ultraviolet light (ca. 280 nm) by proteins. Tyrosine is the only one of the aromatic amino acids with an ionizable side chain.

Detailed explanation-2: -Specifically, the amino acids tyrosine and tryptophan have a very specific absorption at 280 nm, allowing direct A280 measurement of protein concentration. UV absorbance at 280 nm is routinely used to estimate protein concentration in laboratories due to its simplicity, ease of use and affordability.

Detailed explanation-3: -As demonstrated in Figure 2, aromatic amino acids and proteins absorb UV light with two distinct peaks. The peak centered on 280 nm is the result of absorbance by the aromatic ring portion of their structure. The peak at lower wavelengths is caused by absorbance of peptide and carboxylic acid moieties in the compounds.

Detailed explanation-4: -Proteins usually show absorption maxima between 275 and 280 nm (Figure 1), which are caused by the absorbance of the two aromatic amino acids tryptophan (Trp) and tyrosine (Tyr) and, to a small extent, by the absorbance of cystine (i.e. of disulfide bonds).