[Study of molecular dynamics of bovine carbonic anhydrase B by 13C-NMR in two strongly polarizing magnetic fields. I. Intramolecular mobility of polypeptide chains of the native enzyme].

The study of the dynamics of enzyme segmental movement is of considerable importance in the understanding of the physics of the catalytic function of these macromolecules, which cannot be adequately described without introduction of intramolecular mobility of their polypeptide chains. At present high resolution [13C]NMR is mostly used as an effective and selective method for the observation of spectral and relaxation parameters that are sensitive to structure, conformation and local motion. The molecular dynamics of bovine carbonic anhydrase B (carbonate hydrolase EC. 4.2.1.1) in the native form was studied. Measurements of the relaxation parameters (T1, T2 and NOE) of the alpha-carbons of the polypeptide chain in two high magnetic fields (4.7 and 11.7 T) were carried out. The model-free approach of Lipari and Szabo to the interpretation of these experimental data show a satisfactory agreement between theory and experiment for these carbon nuclei if an internal degree of motion such as libration or restricted diffusion in a cone with angular amplitude in the 10 degrees less than theta less than or equal to 20 degrees range and an effective correlation time tau e approximately equal to 6 to 7 x 10(-11) S in addition to the tau R = 3 x 10(-8) S reorientation correlation time of the whole molecular is introduced.