Fourier-Transform Infra-Red Studies of Cytochrome c Oxidase

Kinetic studies using isolated cytochrome oxidase have shown that two distinct functional forms of the enzyme exist (1). The fully oxidised (resting) enzyme, as isolated, oxidises cytochrome c relatively slowly and binds cyanide with low affinity. However, if the enzyme is fully reduced prior to reaction with oxygen for at least one catalytic cycle, then a “pulsed” form is produced in which both cytochrome c oxidation and cyanide binding is markedly increased (1, 2). The “pulsed” form of the enzyme is unstable and, depending on the conditions of incubation, decays back to the resting form within minutes. If the transition between resting and pulsed enzyme were to involve any changes in the conformation of the protein then it might be expected that these changes would also be seen between the oxidised (resting) enzyme and the fully reduced enzyme, since full reduction followed by re-oxidation is one method for producing the pulsed enzyme.