3] CONFIGURATION OF GLOBULAR PROTEINS 57 



is about 3-5 cc./gram, independent of ionic strength. At pH 7, on tiie other 

 hand, the same parameter ranges from 21-2 to 6-7 cc./gram as the ionic 

 strength is increased from 0-01 to 0-55. Corresponding changes were observed 

 in sedimentation and diffusion coefficients. 



A kinetic study of the loss of enzymatic activity of pepsin was performed 

 by Steinhardt'^ as early as 1937. The pH dependence was used as evidence 

 that rupture of specific bonds triggers the reaction. This conclusion is sub- 

 ject to the same comment as was made above for hemoglobin. 



ß-Lactoglobulin. jS-Lactoglobulin undergoes an irreversible reaction above 

 pH 9, the product of which is insoluble at the isoelectric point. The kinetics 

 of the reaction have been investigated by Groves, Hipp and McMeekin.^^ 

 That the product is of the simple polyelectrolyte type is indicated by the 

 titration data for the phenolic groups shown in Fig. 13.^^ 



-40 

 NET CHARGE 



Fig. 13. Logarithmic plot for titration of the phenolic groups of /3-lactoglobulin (Tan- 

 ford and Swanson^«) at ionic strengths 08 (Q) and 0-27 (^). The dashed lines show the 

 slopes of corresponding plots for titration of carboxyl groups (Fig. 12). The difference 

 in slopes is roughly a factor of ten. 



j3-Lactoglobulin is another protein with marked asymmetry about the 

 isoelectric point. The titration data for carboxyl groups, ^^ shown in Fig. 12, 

 are characteristic of a compact protein up to the highest positive charges 

 reached. Viscosity measurement as acid as pH 1-7 also give no indication 

 of any change in configuration. ^^^ In this protein it is thus certain that 

 electrostatic forces alone cannot account for the effect of pH on con- 

 figuration. 



y-Globulin. Jirgensons*" has shown that the viscosity and optical rotatory 

 power of y-globulin depend on pH much like the corresponding properties 

 of serum albumin. His data are shown in Fig. 14. It should be noted that 

 the isoelectric point of y-globulin is considerably higher than that of serum 



