Electrometric and Other Studies of Cytochrome c 391 



results, at least for those derived forms of the protein we have studied, which show 

 pAT values apparently shifting towards the alkaline side as denaturation proceeds. 



I would, however, like to stress that our results with the E^' values for denatured 

 cytochrome c fractions are compatible with the theory that it is not the particular 

 ligands involved that establish the properties peculiar to the cytochrome c haemo- 

 chrome as contrasted with those of an ordinary chemical haemochrome, but rather 

 the native configuration of the protein. This holds not only for the haemochrome 

 properties I discussed following Paleus' paper, but also for the oxidation-reduction 

 potentials. 



Influence of dilhionite on redox potential of cytochrome c 



Henderson: According to Paul {The Enzymes, Academic Press Inc., New York, 1951) 

 dithionite when used to titrate electrometrically cytochrome c gives the low value of 

 +0-12 V instead of +0-26 V obtained with other reductants. This may be the 

 explanation for the similar value of Green {Proc. roy. Soc. B114, 423, 1934) for yeast 

 cytochrome c. 



This would presumably be due to some compound formation with the cytochrome c. 

 Has Estabrook observed any difference in the low-temperature spectra between cyto- 

 chrome c reduced with dithionite and the same material reduced by other means, as 

 they might show such compound formation ? 



Estabrook: We have used mainly enzymic reduction where possible to try and detect 

 any difference in spectra and find that there is no obvious difference between the 

 spectral properties at low temperature of samples of purified haemoproteins reduced 

 enzymically or by dithionite treatment. In the cases of the haemopeptide of cyto- 

 chrome c or the alkaline haemochromes there was, of course, only dithionite reduction 

 employed. 



