GLOBIN AND HEMOGLOBIN AS PROTEINS 247 



mined the sedimentation and diffusion constants for the protein. 

 He conjfirmed the results of the earher workers and showed that on 

 dialysis recombination of a considerable fraction of the protein could 

 occur. Urea, however, slowly denatures hemoglobin (c/. 2115 and 

 Section 4.3.). 



The dissociation of the hemoglobin molecule into smaller units was 

 further investigated by other methods. Tiselius and Gross (2809) 

 and Lamm and Poison (1637) found a diffusion constant of 6.8 to 

 6.9 X 10~^ cm.2 sec.~^ for concentrations of horse carboxyhemoglobin 

 between 0.8 and 3.8%, measured at pH 6.5 in 0.1 M potassium 

 chloride. At lower concentrations (0.2 to 0.4%) somewhat higher 

 values (7.3 to 7.4 X 10~^ cm.^ sec.~0 were obtained. In salt-free 

 solutions, the diffusion constant slowly increased with time. Pre- 

 liminary claims have recently been made (cited in 2711,2721) that 

 hemoglobin dissociates into half molecules in strong salt solutions. 



4.1.3. Myohemoglobin. Working m Svedberg's laboratory Theorell {2759) 

 •was able to show that a slowly sedimenting component (S 20 of 1.9 to 2.1 X 

 10~i5) was present in the heart and kidney of horse and in the skeletal 

 muscles in the cat. Some of his preparations had, in addition, a more rapidly 

 sedimenting component S20 of 4 X 10 ^•'). Measurement of the diffusion 

 constant and of the sedimentation equilibrium did not give reproducible 

 values and Theorell concluded that the smallest particle he found had a 

 molecular weight of about half that of hemoglobin and that the larger com- 

 ponent had approximately the same molecular weight as hemoglobin {2760). 



Subsequent work by Poison in the same laboratory (2166,2710,2721) 

 confirmed Theorell's sedimentation constant for horse myohemoglobin 

 and provided reproducible values for the diffusion constant and the 

 sedimentation equilibrium, which indicated a molecular weight 

 between 16,900 to 17,600. Roche and Vieil (2325) arrived at a figure 

 of 16,850 for the molecular weight by measurement of osmotic pres- 

 sure of myohemoglobin prepared from the skeletal muscle of the horse. 

 Wyman and Ingalls (3137) have recently reviewed the data, and on 

 a basis of additional measurements of viscosity and relaxation time 

 of myohemiglobin (1869) conclude that, if the sedimentation copstant 

 of 2 X 10~^^ is accepted, the maximum molecular weight must be 

 approximately 19,000. 



While it now appears certain that the smallest component in the prep- 

 aration of myohemoglobin from horse heart muscle has a molecular weight 

 one-quarter that of hemoglobin. Theorell's earlier results remain unexplained. 

 He himself considered bacterial contamination as a possible cause of the 

 irregular results obtained when the sedimentation equilibrium was measured. 



