Chinese Journal of Physiology

ACID- AND BASE-BINDING POWER OF PROTEINS 9

Four such tubes were prepared; one was kept as control while the other three were placed in boiling water bath. These tubes was removed, one at a time, from the bath at the end of 5, 10 and 20 minutes; cooled, the lost water replaced, and the pH determined. The pH of the control was 2.92, while those of the solutions heated for 5, 10 and 20 minutes were 3.09, 3.09 and 3.08 respectively. In a similar experiment with ].1 per cent egg albumin using 1.9 cc of N/10 NaOH, the pH of unheated solution was 10.52, while those of the solution heated for 5, 10 and 20 minutes were 10.13, 10.12 and 10.12 respectively.

To determine the complete titration curve of each of the albumins denatured at different reactions would involve a large amount of unnecessary labor. It is sufficient for the present purpose to determine the acid-binding power at some convenient pH on the acid side of the isoelectric point of the protein and the base-binding power at a similar point of the alkaline side. A still simpler procedure is to determine the pH of the solution containing a particular amount of acid or alkali,

In most of the experiments the albumin solution were heated with different amounts of acid or alkali, but before measuring the pH the total acid or alkali contents of all solutions were made the same. The pH’s of these solutions were compared with that of a single solution of natural albumin containing the same amount of acid or alkali as the denatured albumin solutions. If denaturation caused no change in acidor base-binding power the final reaction of the heated solutions should be the same as that of the unheated control. Ifa change occurred, a difference would be found, and the amount of this difference, other things being equal, would depend on the pH of the control chosen for reference, It decreases as the “reference point” is moved away from the isoelectric point, The amount of acid or alkali used in the control solutions was so chosen that the denatured albumin showed no tendency to flocculate and yet not too acid or too alkaline to obscure the change in reaction.

The albumin solutions were prepared from dialyzed crystalline egg albumin. The reaction of the soultion was close to, but probably not always at, the isoelectric point of egg albumin. This condition was, however, not essential, since we were not interested in the absolute values, but rather in the changes, of the acid- and base-binding powers. The concentration of the albumin solutions used was 0.5 to 1.0 per cent,