Fig. 4.
The X-band EPR spectra of the freeze quenched products of the reaction of oxygen with bovine CcO initiated by hand mixing and incubated for 5 min in the presence of natural abundance and isotopically labeled ascorbate. (a) reduction by 10 mM l-[12C] Ascorbate; (b) 10 mM l-[1-13C] Ascorbate. The initial bCcO concentration was 100 µM buffered with 0.2 M sodium phosphate at pH 7.4 containing 0.2% w/v DM. The EPR conditions were the same as in Fig. 3, except the microwave power was 0.3 mW. The simulations (dotted lines) were done with the following parameters. (a) g-values: 2.0068, 2.0066, 2.0023; isotropic spin ½ (proton) hyperfine coupling values Aiso = 1.76, 0.07, 0.19, 0.19 (in Gauss). (b) The same parameters as in (a) with the addition of a spin ½ isotropic hyperfine coupling Aiso of 6.54 G (corresponding to 13C).