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DISCUSSION 

 On the Nature of Cytoplasmic Pigments of Liver Cells 



By B. Chance (Philadelphia) 



Chance: There has been much speculation on the possible function of the cytoplasmic 

 pigment, cytochrome b^, in liver cells, and the desirability of direct experimental data 

 is clearly indicated. We have attempted to determine whether cytoplasmic cytochrome 

 65 is oxidized and reduced simultaneously with the mitochondrial cytochromes. 



; 0.04 



b 440 mg rat 

 iver (wef weight) 



540 550 560 570 

 Fig. 1 . Steady-state oxidized minus reduced difference spectrum for a 

 rat liver slice. (Expt. 708a). 



Liver ^//'ce5— Studies on liver slices can be carried out by a simple modification of the 

 double-beam spectrophotometer (Chance, in Methods in Enzymology, 4, p. 273. 

 Academic Press, Inc., New York, 1957). Thin slices of perfused liver are floated in 

 Ringer's solution in either an oxygen or a nitrogen atmosphere. Figure 1 records the 

 aeiiobic-anaerobic difference spectra of such material. There is a peak attributable to 

 cytochromes c and c^ at 552 m/t and a shoulder caused by cytochrome b absorption 

 at — 562 m/<. There is not, however, any indication that an appreciable portion of 



J 



