Proteins in solution absorb ultraviolet light with absorbance maxima at 280 and 200 nm.
Amino acids with aromatic rings are the primary reason for the absorbance peak at 280
nm. Peptide bonds are primarily responsible for the peak at 200 nm. Secondary, tertiary,
and quaternary structure all affect absorbance, therefore factors such as pH, ionic
strength, etc. can alter the absorbance spectrum.