Kinetics of CO binding to and dissociation from microsomal cytochrome P-450 induced by phenobarbital in rat liver.
The kinetics of CO binding to hepatic microsomes from phenobarbital-treated Sprague-Dawley rats, measured by stopped flow spectrophotometry, can be resolved into three components with second order velocity constants of 2.23 +/- 0.35 X 10(5) M-1 S-1, 1.59 +/- 0.18 X 10(6) M-1 S-1, and 8.7 +/- 1.7 X 10(6) M-1 S-1. The three CO-binding species were present in ratios of 1:1.25:1.39 as judged by the relative amplitude of the change in absorbance at 450 nm associated with each of the kinetic components. Similar results were obtained in a range of [CO] from 10 to 700 micron when CO recombination was followed subsequent to flash photolysis of the CO-associated microsomes. In contrast, the dissociation rate of CO from its cytochrome P-450 complex measured by the NO replacement method was biphasic. Approximately 40% of the bound CO dissociated at a rate of 0.40 +/- 0.071 s-1, whereas the remaining 60% dissociated at a rate of 0.049 +/- 0.008 s-1 at 20 degrees C.
D000818:Animals; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats
D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital