Aromaattisten aminohappojen spektraaliset ominaisuuudet

LÄHDE:  https://www.bio.cmu.edu/courses/03231/LecF04/Lec04/lec04.html 

Maksimiabsorptiokohdat:  tryptofaani 280 nm, Tyrosiini 274 nm, Fenylalaniini 257 nm.DNA vertailun vuoksi: 260 nm.

Spectral properties of amino acids Trp, Tyr, and Phe contain conjugated aromatic rings. Consequently, they absorb light in the ultraviolet range (UV). The extinction coefficients (or molar absorption coefficients) of these three amino acids are:

Amino acid	Extinction Coefficient e (lmax)
Trp	5,050 M-1cm-1 (280 nm)
Tyr	1,440 M-1cm-1 (274 nm)
Phe	220 M-1cm-1 (257 nm)

The amount of light absorbed by a solution of concentration [X] is given by the Beer-Lambert Law:

where

A is termed the "absorbance" of the sample;

I₀ is the intensity of the incident light;

I is the intensity of the light that leaves the sample;

e is the molar extinction coefficient at a specific wavelength, e.g. at l_max;

[X] is the concentration of the absorbing species; and

l is the path length (usually 1 cm).

A solution that does not absorb any light (I=I_o) has an absorbance of 0. A solution that absorbs most of the light that passes through it, has a large absorbance. For example, if 90% of the light were absorbed, I_o/I = 10, and A = 1.0. The above table shows that Trp absorbs UV light the strongest. Furthermore, since both Trp and Tyr show the maximum light absorbance at approximately 280 nm the absorption maximum of most proteins is around 280 nm. In contrast, the absorption maximum for nucleic acids is approximately 260 nm.