The reaction of cytochrome oxidase with cyanide. Preparation of the rapidly reacting form and its conversion to the slowly reacting form.

The magnitude of the slow phase of reaction of cytochrome oxidase with cyanide has been correlated with the size of the epr signal at g' = 12. This epr signal was not found in submitochondrial particles, and significant g' = 12 epr was only observed late in the purification of solubilized enzyme. The Hartzell-Beinert procedure for the purification of cytochrome oxidase (Hartzell, C.R., and Beinert, H. (1974) Biochim. Biophys. Acta 368, 318-338) has been modified so that the purified enzyme reacts in a single rapid phase with potassium cyanide and lacks the g' = 12 epr signal. This enzyme could be converted to the slowly reacting form upon incubation at low pH and/or low enzyme concentration. No procedure for the stable reversal of the process could be found. Some physical and chemical properties of the two forms of the enzyme are compared.