VOL. 12 (1953) 



COMPOUNDS OF FERRICYTOCHROME C 



275 



chrome c in o.i ill HCl causes a decrease of the hght absorption and a shift of the maxi- 

 mum from 395 m/x to shghtly above 400 mjn. In this case we have an isosbestic point at 

 402 m/x. 



Since the change in light absorption was maximal at 395 m/x we made a series of 

 determinations at this wavelength at different hydrogen and chloride ion concentrations. 

 The results are summarized in Fig. 3. 



7 40r 



s. 



"o 



E 



X 



E 



X 



35- 



30- 



■Si 



"0 



E 



X 



X 



ii^O 



20- 



■Si 

 "o 



E 

 X 



« 



E 



X 

 o- 



380 400 420 



Fig. I . Soret band of ferricyto- 

 chromec at different pH values 

 and low [Cl~] . Solutions of cy- 

 tochrome c with a final concen- 

 tration of 4. /^M and varied pH 

 were made by mixing a stock 

 solution of cytochrome c with 

 o.iM HCl and water. The [CI"] 

 thus increased with the acidity 

 in this experiment. 

 pH 3.36 (n), 2.53 (O), 2.20 

 ( + ), 1.87 (x) and 1.70 (#). 



Fig 



360 400 420 



. 2. Soret band of cyto- 

 c in o.io M HCl (#) and 

 after addition of 0.066 

 (O), 0.132 (x), and 0.528 

 ( + ) M NaCl. The total 

 [Cl~] was thus 0.1, 0.166, 

 0.232 and 0.628 respec- 

 tively. 



pH 



Fig. 3. Curves showing how the extinc- 

 tion at 395 m/z varies with pH at dif- 

 ferent [CI"]: 0.009 ( + ). 0.019 (x), 

 0.094 (•)■ 0.189 (o), 0.250 (n), and 

 2.83 (A) M NaCl. 



■Si 

 "o 



E 



X 



E 

 u 



X 



E 



It is seen that variations in pH between 4 and i 

 bring about very great changes in extinction at low 

 chloride concentrations; at increasing [Cl~j the curves 

 more and more approach a constant level of /3* --^ 20-10' 

 cm^ X mole~^. This indicates the formation of a chloride 

 compound of ferricytochrome c in this acid region. 



Fig. 4 shows the variation in light absorption upon 

 the addition of increasing amounts of chloride at pH i.o, 

 2.0 and 3.0. It is seen how the curves at increasing [Cl~] 

 again approach the level fi = 20-10''' cm^ X mole~^. 



Evidently a hitherto unknown compound is formed 

 by the addition of hydrochloric acid or sodium chloride to ferricytochrome c in slightl\' 



In 



fcrj 



Fig. 4. The extinction at 395 

 m/i as a function of [CI"] at dif- 

 ferent pH: 1.0 (x), 2.0 (O), 

 and 3.0 (#). 



/» = 



X - X In 

 a 



-^, where c = concentration in moles/ml ; 

 d = optical depth of solution. 



References p. 282. 



