How is the concentration of protein measured using absorbance?

The concentration of protein is commonly measured using absorbance at 280 nm because this wavelength corresponds to the absorbance maxima of aromatic amino acids, primarily tryptophan and tyrosine, which are highly prevalent in many proteins. When proteins are present in a solution, the aromatic side chains absorb ultraviolet light at 280 nm, and the degree of absorbance is directly related to the concentration of the protein in the solution.

Utilizing this property, researchers can employ the Beer-Lambert law to relate the absorbance to concentration, allowing for quantification of protein levels. This method is widely used due to its simplicity and rapid results, making it a standard in biochemical analyses.

On the other hand, while other wavelengths, such as 260 nm, are often associated with nucleic acids (DNA and RNA) due to their absorbance characteristics, they do not provide specific information about protein concentration. Wavelengths like 310 nm and 320 nm generally do not correspond to significant absorbance of proteins and would not yield reliable data for quantifying protein concentration.