Anomalous T7 Raman spin-lattice relaxation rate of low spin cytochrome P-450 from P s e u d o m o n a s p u t i d a

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Abstract
Electron spin‐lattice relaxation measurements were made on camphor‐free low spin ferric cytochrome P‐450 from Pseudomonas putida. Data were taken between 1.75–13 K at X and Ku band microwave frequencies using the technique of pulse saturation recovery. The experiment revealed an anomalous Raman relaxation rate varying in the low temperature limit as T7 rather than T9, the latter being expected for a Kramers ion. We discuss this anomaly and show how it suggests that the ferric spin system relaxes to thermal equilibrium through interactions with a two dimensional phonon spectrum. The planar structure of the heme complex adds credibility to this interpretation.