Chinese Journal of Physiology

10 H. WU anv T. T. CHEN

The pH of the solutions was determined electrometrically using the quinhydrone electrode as far as possible. When this could not be used the hydrogen electrode was resorted to.

Effect of denaturation of egg albumin without coagulation.—Different amounts of N/10 HCl and N/10 NaOH were added to 25 cc portions of egg albumin solution contained in 25 x 200 mm test tubes. The minimum amount of acid or alkali used was sufficient to prevent coagulation. After mixing, the tubes were weighed to decigram and plunged simultaneously into a boiling water bath. The temperature of the bath dropped to 90° which was maintained for 10 minutes. At the end of this time the tubes were removed and cooled in running water. They were weighed and the loss of water replaced. The required amounts of acid or alkali were added to the tubes to equalize the total acid or alkali content. The volume of the solution was equalized by adding H2O or appropriate mixtures of HCland NaOH. After mixing,

_the pH of the solutions were measured and compared with the unheated control. The results of two experiments are shown in tables 1-2 and figs. 1-2. The point of reference was in table 1 on the acid side of the isoelectric point, and in table 2 on the alkaline side.

It will be noted that there is an increase in pH of the solution as_ the result of heat denaturation when the final reaction is measured on the acid side of the isoelectric point, and a decrease of pH when measured on the alkaline side.

The amount of change in pH increases as the reaction at which the albumin is denatured is further removed from the isoelectric point of this protein (pH 4.8). If the albumin were heated at this reaction it would have been coagulated and the effect of coagulation would be superimposed on that of denaturation. By extrapolation of the curves (dotted lines in figs. 1-2) it can be shown, however, that if albumin could be denatured at the isoelectric point without coagulation, there would be no change in acid- or base-binding power. A more plausible interpretation of this fact is that the albumin is not denatured at the isoelectric point under the conditions of our experiment.