Further observations of the effects of ions on the activity of enzymes

Abstract

Previous communications from this laboratory 1 have made it evident that peptolysis of fibrin is unequal in rate and extent in acid solutions of equipercentage, equinormal (isohydric), equimolecular, or equidissociated (isohydrionic) concentration. The same may be said of tryptolysis of the same protein in a series of bases of analogous concentrations.

We have found that the sequence of zymolysis, both in rate and extent in a given group of acid or basic solutions, varies considerably with the nature of the protein. This fact makes it impossible accurately to formulate statements regarding various phases of peptolysis or tryptolysis without specifying the particular protein involved in the process; it also renders doubtful various general conclusions of common acceptance pertaining to digestion that have been derived, in one research or another, from the use of a single protein. A study of the peptolysis of many proteins in a given series of acid solutions has therefore been undertaken, and an effort will be made to extend the observations to the tryptolysis of the same proteins in a given series of basic solutions.

The speed and extent of both peptolysis and tryptolysis are resultants of conflicting influences. In the case of peptolysis, for example, the hydrogen ions in a given acid solution are always essential and positive factors, whereas the accompanying anions or molecules or both appear to be, as a rule, non-essential and inhibitory factors. This conclusion is warranted by such results as the following, taken from our records of an experiment in which I gram quantities of fibrin were used in IOO C.C. portions of solution at 40° C.:

That acid molecules are not necessarily inhibitory in peptolysis is shown clearly by the appended results of an experiment similar to the one just referred to, but in which acetic acid was used instead of sulfuric acid.