Chinese Journal of Physiology

20 H. WU anp T. T. CHEN

Denaturation of egg albumin by acid.—We have studied also the effect. of denaturation of egg albumin by acid in the cold. Some 1 per cent egg albumin solution was mixed with an equal volume of N/10 HC] and allowed to stand over night. To 20 cc portions of the mixture were added 9.2, 9.0, 8.6, 8.2 and 7.5 cc of N/I0 NaOH. The pH’s of the resulting solutions were 3.63, 3.27, 2.82, 2.57 and 2.38 respectively. The pH’s of the controls, prepared by mixing first the appropriate amounts of HCl and NaOH and then adding the albumin just before the pH determination, were 3.46, 3.17, 2.77, 2.54 and 2.32. These solutions of denatured albumin are thus less acid than those of the natural albumin. The decrease in alkalinity attending denaturation of albumin by alkali in the cold found in our previous study (8) was so large that a confirmation by electrometric methods is not necessary.

Denaturation and coagulation of serum globulin and albumin.—The results of these experiments were in general of the same kind as those obtained with egg albumin, although certain peculiarity of serum albumin is worth noting. An experiment with dog’s serum globulin is shown in table 8 and fig. 8, which is quite comparable with fig. 5 for egg albumin. Tables 9 and 10 and figs. 9 and 10 show the results of two experiments with sheep’s serum albumin. It will be noted that while the change in acid- and alkali-binding power attending coagulation or denaturation by heating on the alkaline side is qualitatively similar to that of egg albumin, the change on the acid side is quite different. Within a considerable range the change in pH is the same, irrespective of the pH at which the albumin is denatured. This behavior is associated with a peculiar property of serum albumin.

Wu and Yen (7) found previously that horse’s serum albumin could not be denatured by mixing a one per cent solution of the protein with an equal volume of N/10 HCl, although denaturation did occur if the acid used was only half as concentrated. This is true even when the solution was heated (8). We have now found that sheep’s serum albumin behaves similarly, but the range of acidity in which no denaturation occurs is wider.

This absence of denaturation is, however, only apparent and not real. When an acid solution of sheep’s serum albumin heated for 10 minutes at 90°C is cooled and neutralized, the solution remains clear. Tf, however, anhydrous sodium sulphate is added to make a concentration of 20 per cent the albumin is partly precipitated. An unheated control under