## Abstract

In the study of protein backbone dynamics by ^{15}N relaxation measurements, an initial estimation of the isotropic global correlation time, τ_{m}, is usually obtained from the average T_{1}/T_{2} ratio of nuclear spins that do not exhibit slow internal motion and with T_{2} values not significantly shortened by chemical or conformational exchange processes. Different methods have been used for identification of the rates of internal motion. However, the number of nuclear spins included in the τ_{m} estimation is often larger than the number that ultimately can be fitted to a single-order parameter, S^{2}, implying that some nuclear spins involved in the initial τ_{m} estimation actually have an effective internal correlation time, τ_{e}, not as fast as assumed. As a consequence, τ_{m} is underestimated, since internal motion reduces the T_{1}/T_{2} ratio. This situation becomes more obvious if the molecule has a large τ_{m} value because the reduction in T_{1}/T_{2} ratio arising from internal motion is more significant than for molecules with smaller τ_{m} and the same degree of internal motion. This Communication describes a more reliable method for identifying nuclear spins which should be excluded from the τ_{m} estimation because of insufficiently rapid internal motion. This results in an improved τ_{m} value, giving a much better agreement between the number of nuclear spins fitted successfully to a single-order parameter, S^{2}, and those used in the τ_{m} estimation.

Original language | English |
---|---|

Pages (from-to) | 347-350 |

Number of pages | 4 |

Journal | Journal of Magnetic Resonance |

Volume | 131 |

Issue number | 2 |

Publication status | Published - 1998 |

Externally published | Yes |

## Keywords

- N relaxation measurements
- Global correlation time
- NOE
- Protein dynamics
- Rate of internal motion