REACTION MECHANISM 489 



does not appear to combine with cyanide or pyridine, nor cruoratin with 

 cyanide, imidazole, or pyridine. Tlie solutions of cruoratin in sodium 

 hydroxide are, however, brown, with an indistinct absorption band at 650 m/z, 

 and differ from those in ammonia in color and light absorption. The facts 

 that cruoratin cannot be extracted with ether, that it contains eight atoms 

 of nitrogen per iron atom, and that the absorption maxima of its compounds 

 are shifted toward shorter wavelengths in comparison with pseudohematin 

 compounds, all indicate that cruoratin is a "hematin c"-like compound. It 

 apparently contains amino acid residues (cysteine?) bound to the side chains 

 and, under certain conditions, may thus be able to form a hemochrome with 

 its own amino groups, as does the protoheme-cysteine adduct of Zeile (cf. 

 Chapter VIII). 



Neither cruoralbin nor cruoratin yielded more than traces of bile pigment 

 with acid. 



6.3. Formation of Similar Green Hemoglobins 

 without Cyanide 



Cyanide is not the only substance which promotes the formation of green 

 hemoglobins of pseudohemoglobin or cruoralbin types, although none of the 

 others causes such a striking reaction. It has been mentioned above that 

 the action of dithionite and atmospheric oxygen alone on hemoglobin slowly 

 produces an absorption band in the orange part of the spectrum. Riedel 

 {2253) observed that pyridine in a concentration of 3-6% accelerated this 

 reaction. Nitrite is able to replace cyanide in the formation of pseudohemo- 

 globin from hemoglobin by hydrogen peroxide, though not effectively {1186, 

 1876,1895)* Recently, Holden {1S20) has found that a large number of 

 substances, e.g., hydrogen ions, ammonia, alcohol, urea, pyridine, iodide, 

 sodium benzoate and salicylate, and phenol, promote the formation of both 

 cruoralbin and pseudohemoglobin (cf. also Jung, 14S9). Some of these 

 substances cause irreversible, but the majority reversible, denaturation 

 ("perturbation"") of hemoglobin. The absorption bands of the carboxy 

 compounds of the cruoralbins thus produced were found at wavelengths 

 3 to 1 1 mij. shorter than those of the corresponding pseudohemoglobins. This 

 indicates that in the formation of cruoralbins the vinyl side chains are attacked 

 by dithionite with formation of "hematin c"' like substances. 



6.4. Reaction Mechanism 



The experiments of Holden {1320) indicate the importance of the 



protein for the reaction. The release of groups in the globin able to 



bind additional protoheme with formation of hemochrome {cf. above) 



also shows that a profound alteration of the type of linkage between 



protein and prosthetic group occurs. Holden assumes that this 



change takes place during the reversible denaturation (perturbation). 



* Kiese {1526b) found this green hemoglobin, however, to be of a distinctly different 

 nature, since it yielded a porphyrin with a carbonyl side chain, and not a bile pignoent, 

 on acid decomposition. 



