protein concentration determintaion - (Apr/14/2007 )

hi,

Does anybody know how to convert the OD value at 280nm for the protein into protein concentration mg/ml. My protein has only single aromatic amino acid and 2 cys residue.

thanks

usually we use Beer-Lambert Law, A = Ecl
so c (the concentration)=A/E.l

Is it really accurate to measure based on spectro? I thought Bradford or Lowry will do a better job in measuring the protein quantity.