NATURE HAS A PART

The Nature and Preparation of Enzymes

A. Laurence Curl, Sigmund Schwimmer.

All the living things contain small amounts of a number of curious chemical substances that assist the cell in performing all its life processes. Their mere presence or contact with the changing contents of the living cell speeds up the chemical reactions that go on there growth, respiration, the metabolism of food. The acceleration seemingly goes on without using up or altering the substances themselves. These accelerators are the enzymes.

Enzymes are made only by living cells. All living cells contain them, for they are essential to life as we know it. Every agricultural product in the natural state therefore contains the enzymes that it made for its own use. Enzymes can often be separated from plant or animal products and used to accelerate chemical reactions in laboratory or factory.

Extracted enzymes greatly speed up certain chemical reactions. They therefore are catalysts, which are substances that hasten chemical reactions without themselves being changed or destroyed in the process. The reactions that are catalyzed, or quickened, are always reactions of value to the cell that made the enzyme.

Enzymes have yet another function. They select one from a number of possible reactions to be speeded up. Often the chemicals in a cell could react together in several different ways. The enzyme determines in which of the ways the reaction will actually proceed. The result of this selective influence is that each reacting chemical in a living organism is transformed by a particular enzyme in a particular way. This directive effect is known as specificity.

In a sense the action of an enzyme is analogous to that of a mechanical corn harvester. Picking corn by hand is slow; the machine hastens the work. But merely to hasten the process would do no good if the corn were spilled on the ground and the stalks put away in the crib. The corn harvester separates the ear from the stalk, then the husk from the ear and sometimes also the grain from the cob, and puts each one in its proper place. The harvester speeds up the process and separates the final products, but it does not, or at least it should not, enter into the final products. At the end of its job it is still, we hope, in as good condition as when it started.

Much labor has been spent to find out how enzymes are produced by living organisms and what the stuff is of which they are made. We have some general ideas, though no facts, on the first point. We know that the characteristics of a living thing are determined by bodies called genes. The genes are transmitted by inheritance and can multiply. Genes are now considered to be the agents responsible for the formation of enzymes. Thus the red color of a rose is due to the presence in the flower petals of a red substance, which is produced from a colorless precursor by the work of one particular enzyme. The enzyme is in turn elaborated by the gene responsible for the production of red color in that variety of rose. When that gene is absent in the flower, the enzyme will be missing and the rose will be white. The gene seems to act like a mold in which the enzyme is produced.

We have much more information on what enzymes are. Chemists have succeeded in extracting, purifying, and sometimes isolating enzymes. Several chemists have received Nobel prizes for work along those lines. All the enzymes whose constitution is definitely known are proteins.

Sometimes the enzyme appears to be a simple protein. Sometimes it is combined with metals, such as iron or copper. Again, the protein is known to be united with other organic substances, the coenzymes, which usually are of simple structure. Curiously enough, vitamins (particularly those of the B complex) often have turned out to be a part of the coenzyme. These facts may explain why a deficiency of vitamins and minerals in the diet causes some form of disease.

Once in a while a vitamin (like niacin) will combine with several proteins to form different enzymes. The enzymes then have an over-all similarity, but an indiscriminate combination of vitamins and proteins as a rule would not lead to substances of any enzymatic activity whatever.

The effects of enzyme action on foods and feeds are discussed in the next chapter. When enzymes stay active after harvesting, the crop is likely to keep poorly; it might even spoil. As a rule, the food processor is interested mainly in getting rid of enzyme action. Usually he does so by heating the material to denature the proteins, as in canning fruits or vegetables. Many enzymes have been found useful in speeding up chemical reactions in industry, however; consequently, methods for their extraction and concentration have been worked out.

Enzymes are utilized in many ways in the production of various commodities.

One way is to treat a substance, such as sucrose (common sugar), with a micro-organism a yeast, mold, or bacterium that contains an enzyme or enzymes which can convert the sucrose into something more valuable. An example is the fermentation of sucrose by yeast to ethyl alcohol and carbon dioxide. The process is involved in the preparation of all varieties of alcoholic beverages and in the manufacture of industrial ethyl alcohol. The carbon dioxide is often utilized in the form of dry ice. Sugars may be converted also into glycerol (glycerin), citric acid, gluconic acid., acetone, butanol, and other valuable products. Alcohol solutions are converted into acetic acid, usually as a dilute solution known as vinegar, when they are treated with bacteria of the genus Acetobacter.

Penicillin is formed by the action of certain molds on a sugar solution. One of the steps in the manufacture of synthetic vitamin C involves the use of bacterial oxidation.

Enzyme preparations, usually much more concentrated than the original material, are often made from bacteria, molds, and yeasts. They are still impure and often contain several enzymes. The preparations are mainly amylases and proteinases, which attack starch and proteins, respectively.

One of the most widely used enzyme preparations is pancreatin, which contains enzymes that react with fats, proteins, and starch. Pancreatin is prepared from the pancreas of hogs or cattle, and is thus a byproduct in the meat-packing industry. The dried and powdered whole pancreas may be used for some purposes. A more concentrated preparation can be made by mincing the glands, mixing with water, and allowing to stand in a moderately acid solution (pH 4 to 5) for 24 hours. The enzymes dissolve and are removed from the solid material by filtering. The filtrate is evaporated to dryness at a low temperature in a vacuum or in a current of air. A! still more concentrated preparation is obtained by adding ethyl alcohol or acetone to the filtrate and filtering and drying the resulting precipitate. Pancreatin is used medicinally as an aid to duodenal digestion and in lienteric diarrhea. It is used commercially in making leather, gelatin, glue, and peptones, and in laundering and dry cleaning to remove proteins and fats. Peptones are water-soluble products formed by the partial digestion of proteins, such as meat, by enzymes. They are used in preparing bacteriological nutrient media.

Pepsin, another commonly used enzyme preparation, is obtained from the mucous membrane of the stomachs of hogs and cattle. It is prepared in much the same way that pancreatin is, except that a much more acid medium is used for the extraction. Unlike pancreatin, pepsin contains only proteolytic enzymes. Pepsin is used medicinally for some stomach deficiencies, for the manufacture of peptones, and in the motion-picture industry to remove gelatin, a protein, from waste photographic films to facilitate recovery of the silver.