How do u find the extinction coefficient of a protein?

Question

e.g. at 280nm alanine is absorbing 0.160 of light, the path length is 1cm i used 0.1mM of alanine.
Any help would be priceless thanx

Answer 1

Alanine is not a protein; that's a detail.

Use definitions::

A = -log (I/I0) = (in your case) - log 0.820 since I/I0 is fraction of light that still gets through

and

A = Ecl where E = molar extinction coefficient, c = concentration (M), l = pathlength (cm).

E has the unlovely units dm^3 mol-1 cm-1

If you are carrying out an experiment, you should use a range of concentrations and get a best straight line for A as a function of c. Better than relying on one reading.