386 Discussion 



However, Minakami (1955, 1956), who also avoided use of TCA, obtained only a 

 single electrophoretic component in his preparation of yeast cytochrome c, which had 

 an iron content of 0-37%, in close agreement with the results obtained in our work. 



In addition to the differences indicated in Table 1, we have observed that solutions 

 of yeast cytochrome c are rather unstable as compared with heart-muscle cytochrome c. 

 Prolonged dialysis against distilled water at 0-2°C may lead to autoxidation of yeast 

 ferrocytochrome c, and the oxidized form is no longer reduced by cytochrome b^ and 

 lactate. Similar results have been obtained with solutions of yeast ferrocytochrome c 



pH 

 Fig. 1. pH/mobility plot for yeast ferricytochrome c and for heart-muscle 

 ferricytochrome c (results from Theorell and Akeson, 1941). 



in the presence of ammonium sulphate. Denaturation of the cytochrome c may occur 

 on oxidation of the reduced form with excess ferricyanide, and also on precipitation 

 from solutions of low ionic strength with acetone at — 10°C. 



The prosthetic group was completely split from native yeast ferrocytochrome c very 

 rapidly by treatment with silver sulphate and 2n acetic acid at room temperature 

 (about 22"C), whereas the reaction with heart-muscle cytochrome c is slow under these 

 conditions, and complete splitting requires higher temperature conditions as described 

 by Paul (1951). However, the product obtained from the yeast cytochrome c appeared 

 to be similar to those obtained by Paul from heart-muscle cytochrome c. 



As shown in Table 1, the absorption bands of yeast ferrocytochrome c at room 

 temperature are displaced slightly towards the blue as compared with the heart-muscle 

 protein, and these differences are even more pronounced at — 190°C (Estabrook, 1956). 

 It is of interest that there is considerable similarity between the absorption spectra at 

 — 190°C of yeast ferrocytochrome c and of the TCA-modified heart-muscle ferro- 

 cytochrome c (Estabrook, 1956; and this publication, p. 444). Yeast ferricytochrome 

 c obtained by Nozaki and co-workers (1957, 1958) was more readily digested by 

 bacterial proteinase than heart-muscle ferricytochrome c. If the haemoprotein used 



