A single protein research integrated advanced biochemistry laboratory course; spectroscopic determination of tyrosyl side chain pKa.

The unique bio-analytical properties of the amino acid tyrosine (Tyr) are the focus of this experiment from the research oriented biochemistry laboratory course at our university. In the present study pK(a(1)), pK(a(2)), and pK(a(3)) values for free Tyr were estimated to be 2.30, 9.40, and 9.97, respectively, when free Tyr was titrated with 1mM NaOH and 1mM HCl using a pH meter. Spectrophotometric analysis of the phenolic side chain pK(a(3)) revealed a value of 10.14, which was consistent with the pK(a)s estimated from the pH meter. The results from this experiment will allow students to compare the free Tyr properties with those present in a protein.