Pigments of rat liver microsomes

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Abstract

The total hemin content of washed rat liver microsomes is 2.15 times the cytochrome b5 content, only a small part being due to bound hemoglobin. The content of flavine is 45 that of cytochrome b5. The flavine probably does not contribute to the DPNH reduced difference spectrum.

The difference spectra of the reduced minus oxidized pigments have been determined. Reduction with DPNH yields only the difference spectrum of cytochrome b5; reduction with dithionite changes this spectrum further, probably due to the reduction of small amounts of methemoglobin. Carbon monoxide forms an intense absorption band at 450 mμ upon reduction of the microsomes by DPNH or dithionite, but no corresponding absorption band in the visible region has been found. The CO 450-mμ absorption appears only to a small extent in preparations containing 2% cholate.

The molecular extinction coefficient of cytochrome b5 has been determined by titrations with DPNH and ferricyanide to be 160 cm.−1 mM−1 for the Soret peak and 20 cm.−1 mM−1 for the α-peak (peak-to-trough values in the difference spectrum).

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    This work was supported in part by the National Science Foundation and the Deutsche Forschungsgemeinschaft.

    2

    Present address: Institute of Physiological Chemistry, University of Marburg, Marburg, Germany.

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