SUMMARY OF SPECTROSCOPIC PROPERTIES 225 



2.4.5. Protein Hemochromes Occurring in Nature. While heme is unable 

 to combine with some native proteins such as egg albumin, some typical 

 hemochromes with protein as nitrogenous base have been found to occur in 

 nature. Cytochrome c, which will be discussed in Chapter VIII, belongs to 

 this category. Another compound of this type is heUconibin, which was 

 detected in 1876 by Sorby in the hepatopancreas of the snail Helix. Heli- 

 corubin has been studied by Krukenberg, MacMunn ("enterohematin"), 

 Dastre and Floresco, Dhere and Vegezzi {587; here the earlier literature is 

 reviewed), Anson and Mirsky {(il), and Roche and Morena {2320). Heli- 

 corubin is a protein protohem/chrome with absorption bands at 571.5 and 

 533.8 my.. The ferric form is stable at pH 5-6. In alkaline solution (pH = 10) 

 only the hemochrome form (absorption bands 56'-2.G and 530. '■2 m^u) is stable; 

 it does not combine with carbon monoxide. 



Another example is the hem /chrome observed by Wigglesworth {3081) in 

 the hemolymph of blood-sucking insects (ef. also Fox, 937a). 



A compound which appears to be a hemoprotein of somewhat similar 

 nature is urechrome, a substance found in the eggs of Urechis caupo, a marine 

 worm. While some of its properties deviate remarkably from those of the 

 better known hemoproteins, the fact that pyridine, alkali, and dithionite 

 produce a hemochrome spectrum with absorption bands at 54.8 and 515 m/i 

 indicates that the prosthetic group is of hematin nature, although not proto- 

 hematin. The side chains may be saturated or of a nature similar to those in 

 cytochrome c. Urechrome is reversibly oxidizable, one equivalent being 

 required {E'o{pR = 7.0, 25° C.) = + 0.185 v., - AE/ApR = 0.06). It was 

 extracted by 0.1 A'^ hydrochloric acid in methanol and appeared to be of low 

 molecular weight (1,700), although this is perhaps due to the breakdown of 

 a larger chromoprotein during the extraction. It is also notable that it does 

 not appear to possess a typical Soret band. Hence its nature carmot yet be 

 considered sufficiently well established (i-i^S). 



With serum albumin, hematin combines to form a hemoprotein, methem- 

 albumin (ferrihemalbumin), which can be reduced to ferrohemalburain. 

 This hemoprotein resembles hemochromes in being oxidized to the ferric 

 state by atmospheric oxygen, but differs from hemochromes by its absorption 

 spectrum. It will be further discussed in Section 3.3.5. 



2.5. Summary of Spectroscopic Properties 



In Table II the position of the maxima and magnitude of the 

 extinction of the absorption bands of the more important hemoglobin 

 compounds are summarized. It will be seen that with a few excep- 

 tions the agreement is as perfect as can be expected for data measured 

 with different types of apparatus and with monochromatic light of 

 different purity. Only in a few instances (cf. Table II, footnotes c 

 and /; and S099) is there any indication that differences in the 

 species from which the hemoglobin was derived may have also 

 played a role in causing differences in the strength of the bands, 



