DENATURED GLOBIN AND OTHER PROTEIN HEMOCHROMES 223 



chrome is formed. The typical two-banded hemochrome spectrum 

 slowly appears with the very sharp maximum at 558 m/n and the 

 weaker and broader band at 528 m/i. Denatured globin hemochrome, 

 like the other hemochromes, is unable to combine reversibly with 

 oxygen, but with carbon monoxide it forms a double-banded spectrum, 

 indistinguishable from that of carboxyhemoglobin. The affinity of 

 denatured globin hemochrome for carbon monoxide is less than half 

 that of hemoglobin. 



2.4.2. Denatured Globin Hemichrome (Kathemoglobin). This 

 compound is formed when hematin is combined with denatured globin, 

 when denatured globin hemochrome is allowed to autoxidize, or 

 when dilute sodium hydroxide is added to hem?*globin or to oxyhemo- 

 globin and the solution is partly neutralized. Solutions of denatured 

 globin hemichrome in weakly alkaline solution are brownish and have 

 the characteristic hemj'chrome spectrum, a weak band at 558 mju and 

 a stronger one at 530 m/x. 



In contrast to Anson and Mirsky {65), Keilin (l-^7o) and Haurowitz {1157) 

 claimed that in alkaline solution denatured globin hem ('chrome is not stable, 

 but dissociates into free hematin and denatured globin. The two-banded 

 absorption spectrum observed in the nearly neutral solution, disappears on 

 alkalinization. In cojitradistinction to the absorption spectrum of hematin 

 in alkali, however, that of "alkaline hematin" obtained from hemoglobin 

 does not show an absorption band in the visible region {99,124.9). King 

 and Delory {1535) also showed the two spectra to be different. The product 

 obtained from hemoglobin showed greater absorption over the whole of the 

 visible range, the difference being least at 610 mju. It is difficult to judge 

 whether this difference can be explained by a different degree of dispersion 

 caused by the protein. With pyridine hemichrome, affinity for the base was 

 not shown to change when the solutions were made strongly alkaline, and it 

 is possible that the spectral change observed with denatured globin hemi- 

 chrome is similar to that accompanying the reaction hemichrome — > hemi- 

 chrome hydroxide (Chapter V, 4.2.) and thus does not indicate dissociation 

 at high pH. 



2.4.3. "Acid Hematin." If the pH of a solution of hemoglobin is 

 made more acid than pH 3-4, the characteristic linkage of the pros- 

 thetic group with the protein is ruptured, while the protein is dena- 

 tured. The purple color of the hemoglobin changes to reddish-brown 

 and shows the rather indistinct two-banded spectrum in the green 

 of heme {1276) protected by protein from flocculation (Holden, 1162; 

 Keilin, 11^75). 



When oxygen is admitted the ferrous iron in the heme is oxidized 



