NMR Titration of Carnosine as a Model Biochemistry Experiment Proton NMR biochemical experiments have appeared in THIS JOURNAL previously (1,2).We wish to presenta modification of one of them (2) in which we substitute the dipeptide carnosine (0-alanyl histidine) for alanine in a pH-NMR titration. Since a dipeptide can serve as a miniprotein, i t has multiple advantages far s pH titration. First, only those protons or - C H y groups of the carbaxyl end titrate with the carboxyl group and only those of the a-and M H z on the -CHa t the amino end of 0-alanine titrate a t the amino pK. This emphasizes the two residue nature of the compound. Second, i t introduces the student t o the histidine residue and allows a third pK, that of the imidazole group, t o be measured. At the concentration used in the experiment P 0 . 2 M )the protons associated with C-2 and C-4 show slightly different pK's. Reflection on this last point together with the study of models should allow the student to visualize the kinds of roles histidine can have in enzyme catalysis. A comparison of papers 3 and 4 illustrate the points above on full proteins and shows how much NMR research has advanced in seven years. Finally, carnosine is readily available and relatively inexpensive. Additional exoeriments usine carnosine are the determination of its metal bindine constants mine the methad of Smith and Albrrtv i . i ) and the recordingot thechangeut pK for the imidarulegruup with temperature which in turn can beused to estinwe the A l l of neurralirlrim fur the buffer. A review of methods to determine rwtal binding properties has been done by O'Sullivan and Smithrrs
