The non-linear dependence of cytochrome P450 activity at low microsome concentration.
Biochem Int 1987 Nov; 15(5):1033-1041
The nonlinear concentration dependence of microsomal cytochrome-P450 dependent activity was explored in intact microsomes, and a possible mechanism for this dependence was suggested. Male Sprague-Dawley- rats were injected intraperitoneally with beta-naphthoflavone at 80mg/kg and sacrificed 24 hours later. The ethoxyphenoxazone- deethylase (EtOPh'ase) activity was decreased in a nonlinear manner following dilution of the liver microsomes into 0.05 molar Hepes at pH 7.6. This decrease upon dilution may be a result of a decrease in the solubility of the lipophilic substrate. When preheated microsomal membranes or synthetic phospholipid was added or when the diluted preparation was reconcentrated, the activity was restored. Vmax values were changed following aqueous dilution of the microsomal fraction. However, only slight changes were seen in Michaelis constant values. The authors conclude that the data are consistent with an earlier suggested model in which the concentration of the catalytically active cytochrome-P450 flavoprotein complex was increased at high phospholipid concentration. The authors caution that differences between model systems and native membrane systems must be considered when attempting to discern the basis for cytochrome-P450 action.
NIOSH-Author; Microsomal-enzymes; Cytochemistry; Enzyme-activity; Laboratory-animals; Membrane-dysfunction; Liver-enzymes; Liver-microsomal-enzymes; In-vitro-studies