Fig. 5.

Line-broadening of Mn²⁺ spectrum after turnover with ¹⁷O₂. The Mn²⁺ spectrum of CcO incubated with 80% enriched ¹⁷O₂ (top trace) shows no broadening, indicating no ¹⁷O₂ is bound at the metal. After 10 msec, which allows for fewer than five turnovers (second trace), severe line-broadening can be seen in all of the fine structure of the spectrum. This broadening was no longer seen after 30 sec of incubation (third trace), indicating that turnover had completed and the product water had escaped by this time. The spectrum of CcO saturated with ¹⁶O₂ and allowed to turn over for 10 msec (bottom trace) demonstrates that the broadening in the samples incubated in ¹⁷O₂ arises from product H₂¹⁷O, not from the reduction of any of the metal cofactors. Experimental conditions are the same as in Fig. 3, except that the resonator used was the TE112 cavity with a resonance frequency of 9.623 GHz.