Electron spin-lattice relaxation of cytochrome P-450 from Pseudomonas putida
Herrick, Richard Charles
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https://hdl.handle.net/2142/25662
Description
Title
Electron spin-lattice relaxation of cytochrome P-450 from Pseudomonas putida
Author(s)
Herrick, Richard Charles
Issue Date
1976
Doctoral Committee Chair(s)
Stapleton, H.J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
electron spin-lattic relaxation
cytochrome P-450
Pseudomonas putida
low-spin ferric cytochrome
relaxation rates
Language
en
Abstract
Electron spin-lattice relaxation measurements have been taken on o
camphor-free low-spin ferric cytochrome P-450 (mo) and the high-spin species of camphor-bound cytochrome P-450 (mos). Relaxation rates were measured at x-and Ku-band frequencies using the technique of pulse-saturation recovery.
The data for the low-spin species revealed an anomalous Raman 7
relaxation rate varying in the low temperature limit as T rather than T9 , the latter being expected for a Kramers ion. This anomaly is discussed and it is shown how the data suggests that the spins relax to thermal equilibrium through interactions with an effective two dimensional phonon spectrum. This hypothesis seems credible in view of the planar structure of the heme ring.
For the high-spin species of substrate-bound P-450, relaxation rates were found to be Orbach-dominated down to temperatures of 1.5 K, with both excited states in the S = 25 manifold contributing to the relaxation rate. The data were therefore fit to two Orbach processes which placed the excited state energies at 9.5 ± 2.8 K and 29.8 ± 1.9 K above the ground doublet for the first and second excited states, respectively. If the two excited energy levels are related to a single ligand field parameter, D, using the constraint imposed by the measured g-values of
the ground doublet, then a fit of the relaxation data gives the values: D = 5.0 ± 0.2 K and E = 0.087D = 0.435 ± 0.02 K. These parameters in turn place the excited doublets at 10.7 ± 0.5 K and 30.5 ± 1.2 K, which are consistent with the constraint-free determination.
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