Chinese Journal of Physiology

8 H. WU anp T. T. CHEN

finding. It should be noted also that he was not studying uncomplicated denaturation but rather coagulation possibly accompanied by some denaturation.*

Wu and Yen (8) found that when egg albumin was denatured by alkali a decrease of alkalinity occurred. A similar, though smaller, decrease of acidity occurred when the denaturation was carried out in an acid solution. Pauli and collaborators (6) have previously found a decrease of alkalinity of an alkaline serum albumin solution on standing. This was attributed by Pauli (6) to an “alteration in state of the alkaline protein”, but it was interpreted by Wu and Yen simply as the result of denaturation. Using a colorimetric method Wu and Yen (7) observed in the case of egg albumin a similar change in reaction as the result of heat denaturation uncomplicated by coagulation.

Harris (3) in the course of an investigation on a hitherto unknown sulphur group in the protein molecule found by formaldehyde titration no detectable change of amino-nitrogen content as the result of denaturation. Mastin and Schryver (5) found, however, an increase in the number of free acid groups without corresponding increase in the aminogroups when egg albumin was denatured by weak acids in the presence of salts.

In view of the confusion between denaturation and coagulation by some authors, the contradictory findings of others and the uncertainty of the colorimetric method for pH determination of protein solutions, a further study of the question with the electrometric method is desired.

EXPERIMENTAL

We have studied the changes in hydrogen ion concentration of protein solutions or suspensions (a) when denaturation occurs without the complication of coagulation, (b) when previously denatured albumin undergoes coagulation, and (c) when both denaturation and coagulation occur. In the first mentioned case the change is due to denaturation alone; in the second case, due to coagulation alone; and in the third to the combined effects of denaturation and coagulation.

It was found early in this study that albumin denatured by heating at different pH’s had different acid- and base-binding powers, although heating for 5, 10 and 20 minutes gave practically the same results. To 30 cc of 0.64 per cent egg albumin 2.5 cc of N/10 HCl were added.

*See the preceding paper for definitions of these terms,