On the Reduced Minus Oxidized Difference Spectrum of P-450 in Liver Microsomes

Abstract

A difference spectrum was observed between dithionite-treated liver microsomes and those treated with NADH under aerobic conditions. The difference spectrum showed two broad peaks at 445 and 555 mμ and a trough at 418 mμ. When microsomes were contaminated by hemoglobin, the peak at 445 mμ was shifted to shorter wavelengths. The intensity of the 445 mμ peak, corrected for hemoglobin, was linearly correlated to the content of P-450 in various microsomal preparations with widely varied contents of the hemoprotein. It was concluded from this and other findings that the dithionite minus NADH difference spectrum corresponds to the spectral difference between the reduced and oxidized forms of P-450. When microsomes were aged under aerobic conditions, there was a decrease in the content of P-450 and a shift of the peak at 445 to 450 mμ.