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E. BOERI, A. EHRENBERG, K. G. PAUL, H. THEORELL VOL. 12 (1953) 



X 



of measurements we derived the following values for the top of the Soret band of Cyt-2H+ 

 at 395 m^ 



pH: 1.70, 1.84, 1.87, 2.06, 2.20 



^395: 46.5. 48.4, 46.4. 51.8. 46.3 



The mean value, 48 {"^ i) • 10' cm^ x mole"^, is in as good agreement as could be expected 

 with the value ^^g^ = 50-10'^ obtained from the points at [Cl~] = o.oog M in Fig. 3. 



The value is exceptionally high for a hemoprotein and of 

 the same order of magnitude as the values for porphyrins 

 in acid solutions^^. The Soret bands of the three com- 

 pounds Cyt, Cyt-2H+-2C1~, and Cyt-2H+ are shown in 

 Fig. 7. 



Magnctometry. ;fm for Cyt was found = 2120 -lO"^ 

 cgs emu. This value is somewhat lower than that found 

 in the earlier investigation** but is probably more correct, 

 since our present preparations were purer than the older 

 ones, and the new value (yu, = 2.24 Bohr magnetons) is 

 in better agreement with the value expected for one odd 

 electron, 1.73 Bohr magnetons + an orbital contribution. 

 The ;fiji for Cyt-2H+-2C1~ was taken from Fig. 5B. 

 It is unexpected that the paramagnetic susceptibility of 

 this compound should vary between pH 1.5 and 3, where 

 the spectrophotometric values remain practically un- 

 changed, but heme-linked groups that are spectrophoto- 

 metrically inoperable, though magnetometrically oper- 

 able, have been reported for other hemoproteins^^' ^2. 

 Whereas the paramagnetic susceptibility between pH 3.0 

 and 1.5 increases only from 6000 to 7400-10"^, and thus 

 remains in the neighbourhood of the theoretical value for 

 three odd electrons, ^(^^ = 6400-10"^, a much more rapid increase in 1^ occurs below 

 pH 1.5, where the light absorption at 395 m/i. begins to decrease (Fig. 3). We believe 

 that these changes below pH 1.5 are connected with the appearance of "type P' in the 

 earlier work^. 



The paramagnetic susceptibility of pure Cyt-2H+ was calculated from six deter- 

 minations at low [Cl~] and pH-values giving the highest possible molar fractions of 

 Cyt-2H+. The values are given in Table I. The mean value of Xm is = 16,200 (=*= 600) • lO"^, 

 corresponding to /x = 6.17 (^ 0.14) Bohr magnetons. This value is somewhat higher than 



380 



400 420 mu 



Fig. 7. Soret bands of Cyt 

 (-1-), measured at pH 5.5, of 

 Cyt-2H+-2C1~ (O), measured 

 at pH 1.5-3.5 and [Cl~] = 

 2.83, and of Cyt-2H+ (#), 

 calculated. 



