Characterization of biomacromolecules by Nuclear Magnetic Resonance spectroscopy
Two proteins were examined by Nuclear Magnetic Resonance (NMR) spectroscopy. The Emb-1 protein of Daucus carota was found to have few spectral characteristics indicative of a stable tertiary structure. In particular, line-widths were narrow, chemical shift dispersion was poor and nuclear Overhauser effect spectra were sparse. The NMR spectra of Ribonuclease A was examined at a range of pH values and the chemical shifts of a selected number of resonances was plotted as a function of the pH. From these titrations curves pKa values were determined and assigned to specific ionizing groups within the protein based, in part, on physical proximity. These pKa values were then subjected to reliability criteria and composite pKa values were determined for 13 of the 15 groups expected to undergo ionization in the pH range followed. Two previously unassigned resonances were assigned to the side chain of an arginine residue involved in a hydrogen bond with a carboxylate. The results of this study were used to evaluate algorithms for the structure-based calculation of chemical shift as well as the calculation of electrostatic properties of a protein.