224 VI. HEMOGLOBIN 



to ferric and "acid hematin" is formed which has a band in the red 

 at 660 m/i with a feeble band in the green. The same compound may 

 be formed when any hemoglobin derivative is acidified, although 

 there are slight differences in its rate of formation from different 

 compounds; it is formed more slowly, for example, from carboxy- 

 hemoglobin. When oxyhemoglobin is acidified, oxidation of the 

 protein in addition to that of the iron atom takes place {1702,2279), 

 and the freshly acidified oxyhemoglobin displays peroxidative prop- 

 erties, which are further dealt with in Chapter VIII, 6.3.6. 



The band of the "acid hematin" in the red lies about 30 m/x nearer 

 the infrared than does the similar band of hematin dissolved in 

 glacial acetic acid (1213). This may be due either to a different 

 degree of dispersion of the hematin, the protein acting as protective 

 colloid {lJf.75), or to the hematin's still being attached to the protein. 

 Although the iron is in the ferric state, it will not readily combine 

 with substances such as hydrocyanic or hydrofluoric acid on account 

 of the low pH. 



2.4.4. Hemochrome Formation from Myohemoglobin. When hydrazine 

 is added to oxyhemoglobin it first reduces the oxyhemoglobin to hemoglobin 

 and then causes denaturation and forms a denatured globin hemochrome. 

 Schumm (24^8) and later Bechtold (197) observed that if myooxyhemoglobin 

 is treated similarly it behaves differently. A spectrum with maxima at 565, 

 552, and 528 m/i can be observed. A similar absorption spectrum appears 

 if 0.1% pyridine + dithionite is added to a solution of myooxyhemoglobin. 

 When the concentration of pyridine or hydrazine is raised, a typical proto- 

 hemochrome spectrum with maxima at 558 and 524 m/x appears. If the 

 pyridine concentration does not exceed 2%, some myooxyhemoglobin can be 

 regenerated from the compound by oxygenation. The compound of myohemo- 

 globin with hydrazine and the first-mentioned compound with pyridine, 

 which on reoxygenation yields myooxyhemoglobin, are substances of the 

 structure A-Fe-B, where Fe represents the heme, A, native (myo)globin and 

 B, hydrazine or pyridine (Gonella and Vannotti, 1019). They are thus allied 

 to the mixed hemoehromes discussed in Chapter V, 4.1. 



In hemoglobin the heme probably lies between two imidazoles (cf. Section 

 3.2.2.) and it is therefore more difficult to form such compounds than in the 

 case of myohemoglobin, where the heme is attached to only dne imidazole 

 and the other coordination point is free (compare the case of formation of 

 cyanhemoglobin and myocyanhemoglobin. Section 2.2.5).. 



Some observations of King and Delory {15So) on the extinction coefficient 

 and band position of denatured globin hemochrome in 20% pyridine suggest 

 that a mixed base hemochrome (denatured globin-Fe-pyridine) may be 

 present, but the observation should be repeated by absolute spectrophoto- 

 metric methods, particularly since it does not appear to agree with observa- 

 tions reported by Drabkin (621). 



