NMR field-cycling relaxation spectroscopy of bovine serum albumin, muscle tissue, Micrococcus luteus and yeast. 14N1H-quadrupole dips.

The frequency dependence of the proton spin lattice relaxation time of bovine serum albumin, muscle tissue, Micrococcus luteus and yeast has been measured by the aid of the field-cycling technique. In all systems 14N1H-quadrupole dips have been observed. The conclusion is that amide groups are the dominating relaxation centers up to approx. 10(7) Hz. This finding can be understood by the fact that protein backbone fluctuations and, if possible, tumbling of the whole molecule rather than side group motions are the relevant mechanisms in this frequency range. A proton relaxation scheme for cells and tissue is presented.