488 X. BILE PIGMENT FORMATION, ETC. 



native from the denatured protein by fractional precipitation with phosphate. 

 Myohemoglobin was converted into similar products. The position of 

 the absorption band of reduced myopseudohemoglobin (myoverdoglobin-CN) 

 was 640 mil, that of its carboxy compound, 636 m^i. These bands thus agree 

 with those of myocholeglobin. 



6.2. Cruoralbin and Cruoratin 



Holden (1315,1318) has prepared compounds similar to pseudo- 

 hemoglobin by exposing hemtglobin cyanide to oxygen in the presence 

 of a large concentration (0.5 M) of well-buffered cyanide and by 

 keeping the iron partially reduced with dithionite. In this way com- 

 plete conversion into a green compound ("cruoralbin") is obtained 

 which remains in solution after dialysis. On the other hand, the use 

 of dithionite in the presence of oxygen entails the danger of conversion 

 into compounds of the "hematin c" type (cf. Chapter V, Section 8.4.) 

 and cruoralbin is possibly a "hematin c" compound corresponding 

 to pseudohemoglobin. 



Properties. The absorption spectrum of ferricruoralbin resembles that of 

 pseudohem?globin rather than of ferricholeglobin; the absorption band at 

 670 m/i of the latter is lacking. The band of ferrocruoralbin was at 624 m/x, 

 that of the carboxy compound at 620-625 m/i. Holden gives position of the 

 absorption band of the alkali-denatured reduced compound as 628 m/x; 

 Lemberg and Callaghan find it at 618 m/x (IGOJ/.). Cruoralbin differs from 

 choleglobin not only by the stability of its iron toward acid, but also by 

 having a distinct Soret band (emM = 77). Holden made the interesting 

 observation that hemochrome linking groups, masked in hemoglobin, are 

 free in cruoralbin. One additional mole of protoheme can be bound by 

 cruoralbin, as indicated by a large increase of the Soret band ( €mM rising from 

 77 to 160). The protein, though soluble at pH 7, is therefore assumed to be 

 no longer unaltered globin, hence the not quite happy name cruoralbin was 

 chosen. 



Cruoratin. Cruoralbin still contains almost the same amount of iron as 

 hemoglobin and binds one molecule of carbon monoxide per atom of iron. 

 If cruoralbin is prepared at 0° C, a substance soluble in organic solvents can 

 be separated from the protein by treatment with acetic acid and amyl alcohol 

 {1318,1319). This is called cruoratin (using the suffix "atin" applied by 

 Schumm for hematin compounds), and considered to be the prosthetic group 

 of cruoralbin. Its ferrous form is called "cruoraem." The yield of this 

 substance from cruoralbin prepared at 18-20° C. is negligible. It is an 

 unstable substance, which is irreversibly oxidized to other substances by 

 ferricyanide and dilute hydrogen peroxide. Cruoraem in ammonia has an 

 absorption band at 610 m/x, shifted by carbon monoxide to 620.5 m/x; and it 

 still has a rather high Soret band (cmM = 70). The fact that the position of 

 this band differs from that of carboxycruoralbin indicates that cruoraem is 

 not the exact prosthetic group of cruoralbin. According to Holden, cruoraem 



