SULFUR CONTENT OF SULFHEMOGLOBIN 493 



was used for three years (1939-1941) at the Pharmacological Institute of 

 BerHn University and which reported 636 m/x as 650 m^i {cf. Kiese and 

 Kaeske, 1527). 



The experiments of Lemberg and co-workers throw some light on the 

 divergencies between the experiments of different authors on the detachment 

 of iron from "sulfhemoglobin." Barkan and Schales (i6'^), who prepared 

 their "sulfhemoglobin" by repeated alternate introduction of hydrogen 

 sulfide and oxygen, found that 20-30% of the sulfhemoglobin iron is split 

 off by acid; carbon monoxide does not inhibit the detachment. Evidently 

 their "sulfhemoglobin" contained much choleglobin and the iron was derived 

 from the latter, not from sulfhemoglobin {cf. also 205 Jf). Haurowitz (1170) 

 who prepared sulfhemoglobin in a milder way by exposure of hemoglobin 

 for ten hours to mixtures of hydrogen sulfide and oxygen, found no easily 

 detachable iron. It is still unexplained, however, why he did not find it in 

 his first experiments, in which sulfhemoglobin was prepared in a manner 

 even more drastic than that used by Barkan. Under these conditions the 

 presence of some choleglobin would be expected; even under the conditions 

 of his later experiments some, though far less, should be present. Barkan 

 and Walker (168) found later that sulfhemoglobin obtained in vivo in rabbit 

 blood did not yield easily detachable iron. The yield from sulfhemoglobin 

 obtained by the action of hydrogen sulfide on oxyhemoglobin was still high; 

 this is probably due to the well-known ease with which the iron of hemoglobin 

 is removed by hydrochloric acid. 



Clarke and Hurtley {■!^5J^) claimed that a compound similar to sulfhemo- 

 globin can be produced by hydrogen selenide. This was not confirmed by 

 Meissner {1896) and Haurowitz (1156), but the latter worked in the absence 

 of atmospheric oxygen. Even if a green compound with an absorption band 

 similar to that of sulfhemoglobin can be produced by hydrogen selenide, it 

 would still have to be shown that the compound is not choleglobin. 



7.5. Sulfur Content of Sulfhemoglobin 

 and Mode of Formation 



Sulfhemoglobin contains one more sulfur atom than hemoglobin 

 (Michel, 1945). This was confirmed by Nijveld {205Jf). The extra 

 sulfur is oxidized to sulfate by bromine, as is the sulfur of thiohistidine, 

 thiourea, and thioamides, and, according to Nijveld, is set free by 

 cyanide and ferricyanide, but not by alkali or acid. 



Harnack {1129) claimed that sulfhemoglobin can be obtained in 

 the absence of oxygen, but Keilin found that oxygen is required and 

 this was confirmed by all later investigators. Since hydrogen peroxide 

 is formed by autoxidation of hydrogen sulfide {2Jf3J^), Michel (194.5) 

 assumed the following reaction mechanism: 



HbO, -I- H2S ^ Hb -f S + H2O2 

 Hb + H.,S + H2O2 -> HbS + 2 H2O 



