The high-pressure stopped-flow technique is applied to study the CO binding in cytochrome P450cam (P450cam) bound with homologous substrates (1R-camphor, camphane, norcamphor and norbornane) and in the substrate-free protein. The activation volume DV # of the CO on-rate is positive for P450cam bound with substrates that do not contain methyl groups. The kon rate constant for these substrate complexes is in the order of 3 · 106 M)1Æs)1. In contrast, P450cam complexed with substrates carrying methyl groups show a negative activation volume and a low kon rate constant of % 3 · 104 M)1Æs)1. .
