Beef heart cytochrome c oxidase contains two cytochromes, a and a3, and Pseudomonas aeruginosa cytochrome c peroxidase has one high- and one low-potential c haem, cHP and cLP. The parallelism in co-ordination and spin states between cytochrome a and haem cHP on the one hand and between cytochrome a3 and haem cLP on the other is illustrated. The two latter haems become accessible to cyanide, whe...
