tains.

THE CHEMICAL NATURE OF ENZYMES

Nothing is known with certainty concerning the chemical nature of enzymes.
Being colloidal in nature, they adsorb carbohydrates, proteins, fats, etc.,
so that active enzyme preparations often respond to the characteristic
tests for these groups of substances; and many investigators have reported
what has, at first, seemed to be conclusive evidence that some particular
enzyme which they have studied is either a carbohydrate, a protein, or some
other type of organic compound. Later investigations have always shown,
however, that if the preparation in question be submitted to the digestive
action of the enzymes which hydrolyze the particular type of substances to
which it is supposed to belong, the material will lose its characteristic
protein, or carbohydrate, etc., properties, without losing its specific
activity, thus clearly indicating that the substance which responds to the
characteristic tests for some well-known type of organic compounds is
present as an impurity and is not the enzyme itself.

The present state of knowledge concerning the nature of enzymes seems to
indicate that, like the inorganic catalysts, they may vary widely in
chemical composition; and that their tremendous catalytic effects are due,
in part at least, to their colloidal nature. This will be better understood
and appreciated after the phenomena associated with the colloidal condition
have been considered (see the following chapter).

NOMENCLATURE AND CLASSIFICATION

Since nothing is known of the chemical composition of enzymes, they can
only be studied by considering the effects which they produce. This is
reflected in the systems which have been adopted for their nomenclature and
classification.

As they were first supposed to be proteins, the earlier representatives of
the group were given characteristic names ending with the suffix _in_,
similar to that of the proteins. Since this idea has been found to be
incorrect, however, a system of nomenclature has been adopted which assigns
to each enzyme the name of the material upon which it acts, followed by the
suffix _ase_. Thus, cellulase is the enzyme which accelerates the
hydrolysis of cellulose; glucase, that acting upon glucose; amylase, that
acting upon starch (_amylum_), etc.

The substance upon which the enzyme acts (or, strictly speaking, the
substance whose hydrolysis, oxidation, or other chem