ABSTRACT
Electron spin relaxation rates over the temperatue range 1.41-15.6 K are presented for the copper-containing protein plastocyanin. Measurements are described for two samples, each derived from a different preparation of equivalent purity, for which the ionic, redox, and protein compositions varied slightly. X-band data are analyzed in terms of a phonon-limited direct process and a Raman relaxation process, where the index of the Raman transport integral is treated as a fitting parameter. Both samples yield rate data at the highest temperatures that are characterized by small deviations from a simple T(n) power law dependence, with n in the range 4.8-5.2. These deviations are most easily quantified when the T(n) power law fits are compared with similar functions that allow for a finite cutoff in the phonon density of states corresponding to Debye temperatures between 90 and 100 K with n in the range 5.0-5.5.
ABSTRACT
The interaction of copper ions with tRNA has been studied by optical and EPR spectroscopies. The interaction results in two different paramagnetic complexes characterized by a tetragonal symmetry of the ligand electric field sensed by the ions. The complete set of the spin Hamiltonian parameters has been extracted by computer simulation with the Monte Carlo method. Hypotheses concerning the putative ligands are put forward.
