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  • Title: Substrates modulate the rate-determining step for CO binding in cytochrome P450cam (CYP101). A high-pressure stopped-flow study.
    Author: Jung C, Bec N, Lange R.
    Journal: Eur J Biochem; 2002 Jun; 269(12):2989-96. PubMed ID: 12071963.
    Abstract:
    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 DeltaV # 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 x 10(6) M(-1) x s(-1). In contrast, P450cam complexed with substrates carrying methyl groups show a negative activation volume and a low kon rate constant of approximately 3 x 10(4) M(-1) x s(-1). By relating kon and DeltaV # with values for the compressibility and the influx rate of water for the heme pocket of the substrate complexes it is concluded that the positive activation volume is indicative for a loosely bound substrate that guarantees a high solvent accessibility for the heme pocket and a very compressible active site. In addition, subconformers have been found for the substrate-free and camphane-bound protein which show different CO binding kinetics.
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