Fig. 3.

Competition assay showing that most of the electrons are conserved in superoxide formation, but that a small fraction of them form hydrogen peroxide directly. In the absence of Cyt c, all of the electrons form H₂O₂. In 150 μM Cyt c superoxide detection is stoichiometric (it outcompetes dismutation). However, ≈10% of the H₂O₂ is not susceptible to Cyt c. Amplex Red oxidation was measured at 557–620 nm (557 nm is an isosbestic point for Cyt c reduction). The curve was calculated by using constant O₂^•− production and simple bimolecular reactions and is illustrative only. CAT, catalase. Conditions were as follows: pH 7.5 and 32°C.