388 Discussion 



in these studies was undenatured, the results suggest that native yeast cytochrome c 

 has a more 'open' folding of the peptide chains than has native heart-muscle cyto- 

 chrome c. 



The major reason for this study was to provide well-characterized, native cytochrome 

 c from yeast for use with crystalline yeast lactic dehydrogenase (cytochrome bo). Both 

 the yeast and heart-muscle cytochrome c were found to be equally reactive with the 

 crystalline yeast enzyme. Both yeast and heart-muscle cytochrome c also react with 

 heart-muscle cytochrome c oxidase preparations, as also found by others (Li and Tsou, 

 1956; Minakami, 1955, 1956). 



The results thus show that both yeast and heart-muscle cytochrome c are closely 

 similar enzymically but have differences in physical and chemical properties which 

 are rather greater than the differences as yet found for cytochrome c preparations from 

 different animal sources. Although the prosthetic groups of yeast and heart-muscle 

 cytochrome c would appear to be similar, there are undoubtedly considerable differ- 

 ences in the secondary protein structure of the two cytochromes. It would appear 

 that the reactivity of the prosthetic group of cytochrome c with other compounds 

 (including enzymes such as cytochrome Zjj) is relatively independent of the folding of 

 the peptide chains of the protein. 



REFERENCES 

 Appleby, C. A. & Morton, R. K. (1954). Nature, Lond. 173, 749. 

 Appleby, C. A. & Morton, R. K. (1959). Biochem. J. 71, 492. 

 Armstrong, J. McD., Coates, J. H. & Morton, R. K. (1958). Abstr. Annual General 



Meeting, Aust. Biochem. Soc., Adelaide, August, 1958; Aust. J. Sci. 21, 119. 

 Ehrenberg, a. (1957). Acta cheni. Scand. 11, 1257. 

 Estabrook, R. (1956). J. biol. Chem. 223, 781. 

 Keilin, D. (1930). Proc. roy. Soc. B106, 418. 

 Leaf, G., Gilles, N. E. & Pirie, R. (1958). Biochem. J. 69, 605. 

 Ll, W. C. & Tsou, C. L. (1956). Acta physiologica Sinica, 20, 50. 

 Loftfield, R. B. & BoNNiCHSEN, R., quoted by Boeri, E. & Tosi, L. (1954). Arch. Biochem. 



Biophys. 52, 83. 

 Minakami, S. (1955). /. Biochem. Tokyo 42, 749. 



Minakami, S., Ishikura, H. & Staako, K. (1956). /. Biochem. Tokyo 43, 575. 

 Morton, R. K. (1958). Rev. pure appl. Chem. 8, 161. 



NozAKi, M., Yamanaka, T., HoRio, T. & Okunuki, K. (1957). /. Biochem. Tokyo 44, 453. 

 NozAKi, M,, MizusHiMA, H., HoRio, T. & Okunuki, K. (1958). /. Biochem. Tokyo 45, 



815. 

 Nunnikhoven, R. (1958). Biochim. biophys. Acta 28, 108. 

 Paul, K. G. (1951). Acta chem. Scand. 5, 389. 

 Paul, K. G. (1951). The Enzymes, Vol. 2, Pt. 2, p. 375. Ed. Sumner, J. B. & Myrback, K. 



Academic Press Inc., New York. 

 Theorell, H. & Akeson, a. (1941). /. Amer. chem. Soc. 63, 1804. 

 Tint, H. & Reiss, W. (1950). /. biol. Chem. 182, 385. 



Properties of Native Cytochrome c 



HoRio: I would like to make a comment on the properties of cytochrome c. 



As found by Margoliash, native cytochrome c can be separated easily from modified 

 cytochrome c by resin chromatography. Of the modified cytochrome c fractions, 

 some fractions show the same absorption spectra as native cytochrome c. 



One can recognize easily which cytochrome c is native, by comparing various 

 extraction- and purification-procedures, by comparison of the properties (ascorbate- 

 oxidizing activity, redox-potential, etc.) and by comparing the properties of each 

 sample after treatments such as lowering and raising pH, or heating. 



In the oxidized state, native cytochrome c is rapidly digested by a bacterial proteo- 

 lytic enzyme. The modified cytochrome c is much more rapidly digested. This fact 



