Biochemistry 4th Edition by Reginald Garrett, Charles Grisham

Exercise 13

Determining tyrosine content of an unknown protein
A previously unknown protein has been isolated in your laboratory. Others in your lab have determined that the protein sequence contains 172 amino acids. They have also determined that this protein has no tryptophan and no phenylalanine. You have been asked to determine the possible tyrosine content of this protein. You know from your study of this chapter that there is a relatively easy way to do this. You prepare a pure 50 µM solution of the protein, and you place it in a sample cell with a 1 cm path length, and you measure the absorbance of this sample at 280 nm in a UVvisible spectrophotometer. The absorbance of the solution is 0.372. Are there tyrosines in this protein How many (Hint: You will need to use Beer's Law, which is described in any good general chemistry or physical chemistry textbook. You will also find it useful to know that the units of molar absorptivity are M -1 cm -1.)