Of the Substrate Concentration on T H E Rate of Hydrolysis of Proteins by Pepsin

In contrast to the numerous papers on the influence of changes in the pepsin concentration, the influence of varying the protein concentration on the rate of digestion of protein has been but little studied. Weis ~ found that the rate was nearly directly proportional to the protein concentration in low concentration but increased more slowly than the latter in concentrations of more than 2 to 3 per cent. The experiments were made with a crude enzyme preparation which contained several proteolytic enzymes, and were made in such a way as to compare the changes in different solutions after the same time interval, instead of comparing the times required to cause an equal change. They are therefore difficult to interpret. Preliminary experiments made with a purified pepsin and purified egg albumin showed in general the same results as those found by Weis. In concentrations of more than 2 to 3 per cent the rate of digestion increases more slowly than the protein concentration and finally becomes nearly independent of it. This phenomenon is a v ~ y general one in enzyme reactions and many explanations have been offered to account for it. Brown s suggested that the relative decrease in the rate of digestion with increasing substrate concentration was due to the fact that the enzyme remained combined with the substrate for a period of time large compared with the time necessary for combination to take place. The enzyme therefore becomes more and more "saturated" with substrate as the relative concentration of substrate to enzyme increases. Van Slyke and Cullen 3