Recent developments in the 13C NMR spectroscopic analysis of paramagnetic hemes and heme proteins

Despite the wealth of information that has been obtained from the study of paramagnetic hemes and heme proteins by 1H NMR spectroscopy, there are certain limitations imposed by the nature of paramagnetically affected resonances that are difficult to overcome. Although it has long been recognized that 13C NMR spectroscopy is likely to be a powerful complementary technique to overcome some of these limitations, the low sensitivity and low natural abundance of 13C nuclei has resulted in a lag in the application of 13C NMR spectroscopy to the study of paramagnetic hemes and heme proteins. The tremendous advances in methodology and instrumentation witnessed in the NMR field, coupled to the advent of recombinant DNA methods that have made possible the preparation and purification of significant quantities of proteins, and the biosynthesis of 13C-labeled heme, have contributed to an increased interest in the study of paramagnetic heme active sites by 13C NMR spectroscopy. As a consequence, 13C NMR spectroscopy is emerging as a powerful tool to study heme electronic structure and structure-function relationships in heme-containing proteins. In this report we strive to summarize some of the recent developments in the analysis of paramagnetic hemes and heme-containing proteins by 13C NMR spectroscopy.