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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. Above is only for polypeptides without co-factors. But a lot of proteins have some other factors. Hemoglobin is the typical samples for this. The heme in hemoglobin has a great absorbency at around 420 to 430 nm, also has peak absorbency at around 500, 540 nm, 578 and 634 (if the iron is ferric) or at around 543 and 577 (if iron is ferrous, oxygenated).For other proteins,such as cytochrome proteins, P450, they also are able to absorb visible light. |
