Cytochromes Cooled in Liquid Nitrogen 



443 



Modified Cytochrome c of Heart Muscle 



The extreme in modification of a- and /5-band splitting is observed when 

 one determines the spectrum of the peptide core of cytochrome c (Ehrenberg 

 and Theorell, 1955). This is shown in Fig. 6 (Note 4). Included with the 

 spectrum of digested and reduced cytochrome c is a spectrum of alkali- 

 modified cytochrome c as well as that of biologically-active heart muscle 



TCA Treuied Cytochrome C 



1 I I I I I I I I ' I I 



490 520 550 



Wavelenglh (mp) 



Fig. 7. Spectra of trichloroacetic acid-modified cytochrome c. Samples of 

 horse heart cytochrome c, obtained from Dr. Margoliash, were treated as 

 described in Fig. 4. Curve A represents fraction la while Curve B represents 

 fraction He as obtained from the ion exchange resin IRC 50 during the purification 

 of cytochrome c. 



cytochrome c. One sees with the peptide core a single a-band, broad and 

 symmetrical, with indications of a Ca^g-band at 536 mfx. The presence of a 

 complex /9-band is apparent but the many small bands generally observed 

 with the undigested cytochrome c are not detectable. Alkali-treated cyto- 

 chrome c has also lost much of the fine band structure. Of interest is the 

 1-5 m/^ difference in absorption band maxima between the two modified 

 samples. The spectrum of the peptide core of cytochrome c resembles most 

 closely the alkaline haemochrome of reduced cytochrome q (see below). 



Figure 7 shows the extremes of a series of samples which we were fortunate 

 to obtain from Dr. Margoliash. These represent the first (A) and the last 

 (B) of a series of six fractions of cytochrome c obtained from IRC 50 resin 

 (Margoliash, 1954a) during the purification of horse heart cytochrome c 

 prepared by the conventional Keilin and Hartree (1945) method. Margoliash 



