Outline the property of protein which has been used for its estimation at 280nm

The property of proteins commonly used for estimation at 280nm is their absorption of ultraviolet (UV) light due to the presence of aromatic amino acids, primarily tryptophan and tyrosine. This phenomenon is based on the fact that these aromatic residues have specific absorbance spectra in the UV range, with maximum absorption occurring around 280nm. This property has been widely utilized for the quantification and characterization of proteins. Here's an outline of the key aspects:

1. Absorption by Aromatic Amino Acids:

   • Tryptophan and tyrosine residues in proteins have characteristic absorbance spectra in the UV range.
   • These aromatic residues absorb light with maximum absorption around 280nm due to the electronic transitions within their aromatic rings.

2. Beer-Lambert Law:

   • The Beer-Lambert law states that the absorbance of a sample is directly proportional to the concentration of the absorbing species and the path length of the sample.
   • This law is commonly used for quantification based on absorbance measurements.

3. Quantification of Protein Concentration:

   • Since the absorption of UV light at 280nm is directly related to the concentration of aromatic amino acids in proteins, it can be used to estimate protein concentration.
   • The absorption at 280nm is proportional to the protein concentration, allowing for the determination of protein concentration in solution.

4. Limitations and Considerations:

   • The accuracy of protein quantification at 280nm can be affected by factors such as the presence of other absorbing species in the sample, such as nucleic acids or contaminants.
   • Proteins with different compositions of aromatic amino acids may have different molar absorptivities, affecting the accuracy of quantification.
   • Corrections or adjustments may be necessary to account for these factors in protein quantification protocols.

5. Applications:

   • Protein quantification at 280nm is widely used in biochemical and biotechnological research, protein purification, and quality control in protein production processes.
   • It is commonly used alongside other methods such as Bradford assay, Lowry assay, or bicinchoninic acid (BCA) assay for accurate protein quantification and characterization.

In summary, the absorption of UV light at 280nm by aromatic amino acids in proteins provides a convenient and widely used method for the estimation of protein concentration in solution, based on the Beer-Lambert law and the specific absorbance properties of aromatic residues.