[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]. / Izuchenie molekuliarnoi dinamiki v karboangidraze B krupnogo rogatogo skota metodom 13C-IaMR v dvukh sil'nykh poliarizuiushchikh magnitnykh poliakh. I. Vnutrimolekuliarnaia podvizhnost' polipeptidnogo ostova v nativnom fermente.

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.

[Study of bovine carbonic anhydrase by 13C-NMR-spectroscopy]. / Issledovanie karboangidrazy v krupnogo rogatogo skota metodom 13C-IaMP-spektroskopii.

The study of internal mobility in enzymes is of considerable importance for the understanding of their catalytic function, which cannot be adequately described as a property of a rigid protein. [13C]NMR spectroscopy permits simultaneous and selective observation of spectral lines from carbon atoms in many different residues in the enzyme with the chemical shift and relaxation parameters sensitive to structure, conformation and local motion. The changes in internal mobility in bovine carbonic anhydrase B (carbonate hydrolase, EC 4.2.1.1) in the native form and at various stages of denaturation are studied. Measurements of the relaxation parameters (T1, T1 rho) and of the NOE of 13C nuclei in the native protein showed that the extensive beta-sheet together with groups in the active center has a considerable internal librational mobility with tau G about 10(-11) s. This librational mobility is fairly uniform for all the alpha-carbons in the native enzyme. The use of a semiempirical modification of the motional theory proposed by Woessner allows to use simultaneously all the relaxation parameters measured in order to determine reliable values of the various correlation times.