262 VI. HEMOGLOBIN 



globin. The comparison between the behavior of different systems 

 frequently provides a crucial test for a given theory. We shall not 

 discuss all the theories put forward but only those still of interest 

 today. Much of the early work has been dealt with by Barcroft {HI). 



5.1.2. Hiifner's Equation. The first attempt to describe the disso- 

 ciation curve was that of Hufner (1355). After satisfying himself 

 that one molecule of oxygen combined with one atom of iron, he 

 expressed the equilibrium in terms of the law of mass action : 



K= [HbO.] 



[Hb] [O2] 

 from which: 



y = — — - — 

 1 + Kp 



may be derived, where y is defined as [Hb02]/[Hb02 + Hb], p is 

 the partial pressure of oxygen, and K, the equilibrium constant. 



While Hiifner's equation does not describe the type of dissociation 

 found in blood or in concentrated hemoglobin solutions, it does 

 describe the dissociation of denatured globin carbon monoxide hemo- 

 chrome (66), the gaseous equilibria of myohemoglobin (1279,2762), 

 and the equilibrium between oxygen and Gastrophilus hemoglobin, 

 which has a molecular weight of 34,000 and contains two hemes 

 (1503a). In addition, the well-known equation: 



[HbCO ] _^[C0] 

 [HbOs] [O2] 



where K represents the ratio of the affinity of hemoglobin for carbon 

 monoxide and oxygen, is a special case of Hiifner's equation (1103). 

 This equation holds even for blood. The implications of the equation 

 are further discussed in Section 6. The equilibrium between hemo- 

 globin and either oxygen or carbon monoxide and ability of the 

 equation to describe the behavior of the more complicated system 

 when both gases are present will be discussed later. 



5.1.3. Hill's Equation. The failure of the simple Hiifner equation 

 to describe the dissociation curve of Hb02 led to a number of modified 

 theories. In one of these, put forward by A. V. Hill (127 J^), the unit 

 containing 1 atom of iron was capable of polymerization to a rather 

 indefinite size. Hill's theory is no longer held in its original form, 



