Abstract

CRYSTALLINE pepsin, in solutions of constant ionic strength on the alkaline side of its stability maximum, inactivates unimolecularly at a rate which is inversely proportional to the fifth power of the hydrogen ion concentration. This unusual relationship has been demonstrated over a velocity interval of 1 to 5,000 in nearly a hundred kinetic experiments at two temperatures with four different buffers. The rate varies with the buffer, but the fifth-power relation does not. As the buffer ratios change by different amounts in the same pH range, general basic catalysis is therefore excluded. It is likewise improbable that simple hydroxyl ion catalysis determines the rate.

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