Effect of substrate on the spin state of cytochrome P-450 in hepatic microsomes |
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Authors: | M R Waterman V Ullrich R W Estabrook |
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Institution: | Department of Biochemistry, The University of Texas Southwestern Medical School at Dallas, Dallas, Texas 75235 USA |
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Abstract: | The effect of substrate on the spin state of oxidized cytochrome P-450 in liver microsomes prepared from phenobarbital-pretreated rats has been examined. Formation of the substrate-induced Type I difference spectrum was found to correlate quantitatively with the disappearance of the ferric low-spin esr signal of cytochrome P-450. The dissociation constant of substrate for oxidized cytochrome P-450 obtained by optical methods was found to be the same as that obtained from esr methods provided that the same high microsomal protein concentration was used. However, a decrease in microsomal protein concentration leads to an apparent increase in the affinity of substrate for oxidized cytochrome P-450, indicating a dependence of lipophilic substrate dissociation constants on the membrane concentration. |
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