Kinetics of elementary steps in the cytochrome P-450 reaction sequence. II. Temperature dependence and species differences in substrate binding reaction.

Species dependencies and the temperature function of substrate binding reaction have been studied. The solubilized P-450 preparations from rat and rabbit, respectively, exhibit similar substrate binding characteristics with respect to rate constants and substrate specificity. The rabbit P-450 is more sensitive to preparational disintegration, this holds especially for aniline. In the Arrhenius plots a normal temperature dependence without breaks is observed. Iron ligands are bound with relatively low activation energies and negative entropies. The parameters increase for benzphetamine (type 1) and further for aniline (type 2), the latter substrate being entropically favoured too.