Abstract
Several of the carboxyl C atom resonances of hen egg-white lysozyme (mucopeptide N-acetylmuramoyl hydrolase, EC 3.2.1.17) were resolved by 13C-NMR at 68 MHz. The change in chemical shift of the carboxyl C atom resonances, as a function of pH, enabled the distinction of these resonances against the background of many nontitrating carbonyl group resonances. Several apparent microscopic ionization constants were determined from the carboxyl group NMR titration curves, and possible assignments are discussed. Preliminary experiments were carried out in the presence of Co2+, and selective shifts of several resonances were observed. The direct observation of a wide range of single functional groups of proteins in solution may be possible by NMR techniques.