Studies on P-450. III. On the Absorption Spectrum of P-450 in Rabbit Liver Microsomes

Abstract

Liver microsomes were obtained from both phenobarbital-treated and untreated rabbits, and used for the studies on the spectral properties of P-450. The absorption spectra of the control and the induced microsomes were measured using, as the reference of spectrophotometry, the microsomes which were decolorized by the hydrogen peroxide-treatment. spectrum of the induced components was obtained by taking the difference spectrum, induced minus control, with the preparations which were so adjusted as to contain the same amount of cyto-chrome b₅. The approximate absorption spectrum of P-450 in liver microsomes was obtained photometrically by subtracting the spectrum of the preparation, which had been subjected to a prolonged aerobic treatment with pCMB, from the spectrum of the untreated control. The resulting spectrum showed essentially the same characteristics as that of P-450 in adrenal cortex mitochondria. The nature of the colored prosthetic group of P-450 and the limitation in the accuracy of measurement performed in the present study were discussed.