494 X. BILE PIGMENT FORMATION, ETC. 



This was supported by the observation that hydrogen peroxide or 

 perborate also formed "sulf hemoglobin." It has been shown above, 

 however, that these reagents cause the formation mainly of chole- 

 globin, not of sulf hemoglobin. Nijveld has also pointed out that 

 Michel's formulation does not agree with this statement that at low 

 sulfide concentrations only one mole of sulfide is required for the 

 formation of one mole of sulfhemoglobin.* Nijveld formulates the 

 reaction as follows: 



Hb + H2S -^ Hb • H2S 



Hb02 + Hb • H2S -> (Hb— 2H)S + Hb + 2 H2O 



According to him, sulfhemoglobin would contain two atoms of hydro- 

 gen less and one atom of sulfur more than hemoglobin. The fact 

 that no more than 75% sulfhemoglobin can be obtained in the reaction 

 is explained by Nijveld by the assumption that the complex: 



(Hb— 2H)S— (Hb— 2H)S 



I I 



(Hb— 2H)S— Hb02 



can no longer react with HoS according to the second of the above 

 equations, at least not intramolecularly. 



While this explanation is in agreement with Nijveld's own experi- 

 ments, it still fails to explain the results of Michel. At least a second 

 mole of sulfide would be required for the formation of the hemoglobin 

 from oxyhemoglobin, with which the reaction of Nijveld as well as 

 that of Michel begins. Also, interaction between hemes does not 

 appear necessary for sulfhemoglobin formation {cf. Section 7.7.). 



If Michel's results are correct the over-all equation must be written 



HbOj + H2S -^ (Hb— 2H)S + 2 H2O 



Nijveld suggests that the two hydrogen atoms removed from 

 hemoglobin in the reaction are derived from the prosthetic group. In 

 the discussion on the structure of the latter it will be seen that this is 

 hardly possible. It is much more likely that the hydrogen is taken 

 from a hydrogen donor group in the globin, and that the reaction is 

 to be written : 



Hb(XH2)02 + H2S -> Hb(X)S + 2 H2O 



In spite of the fact that hydrogen peroxide in vitro forms pre- 



* We have not found any clear-cut experimental proof for this in the papers of 

 Michel or Nijveld. Neither mentions sulfide analyses. How Michel arrived at his 

 conclusion is not evident from his publication; Nijveld only showed that one molecule 

 of oxyhemoglobin yielded one molecule of sulfhemoglobin as long as hemoglobin was 

 also present. 



