502 CHEMISTRY OF THE PROTEIDS CHAP. 



a salt-like combination formed between the blood pigment and the 

 dilute ammonia, in which haematin was dissolved before being reduced 

 with hydrazin. The same observation was first made by Zeynek. 1 



Carbohaemoglobin or C0 2 Hb 



Under this name Bohr 2 has described a number of loose com- 

 pounds formed between different amounts of C0 2 and a given 

 quantity of haemoglobin. None of these compounds has, however, been 

 prepared in a pure state. According to Torup, 3 carbohaemoglobin 

 shows an absorption-band at A.553, while the band of reduced haemo- 

 globin possesses its maximum intensity at A559. Cohnheim says that 

 C0 2 Hb cannot be classed along with such compounds as COHb or 

 NOHb, because C0 2 and 2 do not mutually replace one another (see 

 below), and as the power of absorbing C0 2 is even greater than that 

 of uniting with 2 . The C0 2 Hb dissociates even more readily than does 

 oxyhsemoglobin. Bock 4 and Bohr have further pointed out that both 

 COHb and MetHb can bind C0 . Cohnheim believes that haemo- 

 globin is partly converted into ' acid-hemoglobin ' by the action of 

 C0 2 , but acid-ha3moglobin, as pointed out on p. 496, being in all prob- 

 ability acid-haematin, it would follow that C0 2 is able to cause a tem- 

 porary dissociation between the haematin and the globin radicals, a 

 point of great interest in connection with the C0 2 carrying-power of 

 haemoglobin (Mann). That C0 2 and 2 under certain conditions 

 do react upon one another has been shown by Bohr and his pupils, 

 see p. 489. 



Nitric Oxide-haemoglobin 



Haemoglobin forms also a compound with one molecule of nitric 

 oxide, NO, as first described by Hermann. 5 The affinity of NO for 

 haemoglobin is even greater than that of CO, and therefore CO is 

 driven out of its combination with haemoglobin by NO, a fact which 

 Hiifner, Kiilz, and Marshall have made use of in determining the 

 amount of CO in combination with haemoglobin. 



Kisskalt 6 first noticed that meat becomes red when it is boiled in 

 water containing a nitrite, and suggested that the red colour of salted 



1 Zeynek, Zeitschr. f. physiol. Chem. 25. 492. 



2 Chr. Bohr, Festschrift fur Ludwig, p. 164 (according to Malys Jahresber. /. Tier- 

 chem. 17. 115) (1887) ; Skandinav. Arch. f. Physiol. 3. 47 (1891) ; 8. 161 (1898). 



3 Sophus Torup, Holy's Jahresber. f. Tierchem. 17. 115 (1887). 



4 Job. Bock, Scandinav. Arch.f. PhysioL 8. 363 (1898). 



5 L. Hermann, Arch.f. (Anat. u.) Physiol. 1865, p. 469. 



6 Kisskalt, Arch. f. Hygiene, 35. 11 (1899). 



