The identity of pulsed cytochrome oxidase

Reduction and reoxidation of beef heart cytochrome oxidase, under conditions that ensure the strict absence of hydrogen peroxide, produce a fully oxidized form of the enzyme that has the Soret band at 420 nm, as opposed to the 428 nm band normally associated with the pulsed or oxygenated enzyme. The 420 nm form shows the enhancement of catalytic activity associated with the pulsed enzyme. Addition of hydrogen peroxide to the 420 nm form gives rise to the 428 nm band of the oxygenated enzyme, thereby clearly establishing that the 428 nm form is a peroxide derivative of the fully oxidized enzyme. Previous data from other groups are re-evaluated in the light of our experiments.