PROPERTIES OF FERROUS COMPOUNDS 217 



stable. Stitt and Coryell (2669) found the unstable cyanide compound to be 

 dianiagnetic and assumed it to have the same type of structure as carboxy- 

 hemoglol)in, with covalent bonds. Holden (1315) observed that the .spectrum 

 was typical of a hemochrome. He concluded that the substance was a native 

 globin hemochrome similar to that prepared by Hill {1275) and that cyanide 

 was not combined with the heme. Kiese and Kaeske {1527) however, 

 observed that myohemoglobin reacts to form a cyanide compound and that 

 in 20% urea at ;>H G.8 hemoglobin likewise reacts with cyanide. These 

 observations cannot be reconciled with Holden's view, and we conclude that 

 a true cyanhemoglobin exists. In hemoglobin the distal imidazole group 

 (Section 3.2.2.) may compete with the cyanide and render the compound 

 unstable. No such reaction takes place with myohemoglobin. In the pres- 

 ence of urea the structure of hemoglobin is altered and the competing influence 

 of the imidazole weakened. 



The myocyanhemoglobin compound can be considered related to the 

 mixed native globin pyridine hemochromes which Kiese and Kaeske obtain 

 from myohemoglobin {cf. Section 2.4.4.). 



2.2.6. Carbylamine Hemoglobin (HbCHsNC). This compound was first 

 observed by Warburg in 1929 (2950). He observed that the dissociation of 

 carboxyhemoglobin was diminished by the presence of methylcarbylamine, 

 but that the light sensitivity of the reaction was increased. He concluded 

 that both carbon monoxide and carbylamine were bound to the hemoglobin 

 and observed a slight difference between the absorption spectra of "carbon 

 monoxide-carbylamine-hemoglobin" and carboxyhemoglobin. This is prob- 

 ably another example of the Haldane effect (Section 5.2.2.), which may 

 operate in all complex hemoglobin systems; if hemoglobin is partially satu- 

 rated with carbon monoxide, the affinity of the remaining hemoglobin for 

 oxygen is increased. In the same way, the linkage of methylcarbylamine to 

 one or two of the hemes in the hemoglobin molecule may increase the 

 affinity of the remainder for carbon monoxide. Hemoglobin itself, however, 

 has a much weaker affinity for methylcarbylamine than for oxygen or carbon 

 monoxide. 



The spectrum of carbylamine hemoglobin is remarkably similar to that of 

 cyanhemoglobin, the maxima in the visible region lying at about 565 and 

 530 m;u. The magnetic susceptibility of methylcarbylamine hemoglobin 

 has not been measured, but the related ethylcarbylamine compound, which 

 has a similar spectrum with sharp bands lying at 554 mu and 525 m/i, has 

 no unpaired electrons and therefore covalent bonds {2397). 



2.2.7. Nitrosobenzene Hemoglobin. Loeb, Bock, and Fitz {17C)9) in 1921 

 obtained a violet hemoglobin compound while investigating nitrobenzene 

 poisoning. It has been shown by Jung {lJ^If.lJJ^.I^3) and Keilin and Hartree 

 {1490) to be nitrosobenzene hemoglobin. The compound has two weak 

 bands at 567 mu and 543 mu. Nitrosobenzene can displace oxygen and carbon 

 monoxide from their combination with hemoglobin, but if the ])artial pressure 

 of carbon monoxide is increased sufficiently, it again replaces the nitrosoben- 

 zene. Other aromatic nitroso compounds are able to form hemoglobin com- 

 pounds. Jung and Keilin and Hartree have shown that nitrosobenzene 



