| Abstract: | The longitudinal 13C spin relaxation times T1 and the 13C{1H} nuclear Overhauser enhancement were measured in a concentrated aqueous solution of the basic pancreatic trypsin inhibitor. The correlation time for overall rotational motions of the basic pancreatic trypsin inhibitor molecules was found to be τR ≈ 2 × 10?8 s. In connection with previous 1H n.m.r. studies of intramolecular motions of the aromatics, we were particularly interested in the correlation times τG for intramolecular segmental motions of the aromatic rings. The present experiments revealed no manifestation of intramolecular motions of the aromatics, indicating that τG ? 2 × 10?8 s for the aromatic ring carbon atoms. On the other hand, rapid segmental motions were evidenced for the peripheral carbon atoms of aliphatic amino acid sidechains. Comparison of the 1H and 13C n.m.r. data on the basic pancreatic trypsin inhibitor indicates that the time scale of high resolution 1H n.m.r. at high fields may in many instances be more appropriate for studies of the molecular dynamics in globular proteins than the time scale of spin relaxation measurements. |
