Science in Christian Perspective
A relatively new branch of science, biochemistry, is concerned with the chemistry of life or what makes us tick and enzymes are those compounds responsible f or this ticking. In f act, J. B. Summer, the f irst to isolate an enzyme in crystalline form (1), defines life as "an orderly functioning of enzymes" and disease as "a disorder, inhibition, or hyperfunction of enzymes" (3).
These very essential compounds are present in all living cells as well as cellular excretions such as saliva, gastric juice, milk, plant sap, etc. In the cell, enzymes are either dissolved in the cytoplasm or are bound to particulate components such as microsomes and mitochondria. Sumner has estimated that "the average concentration of each individual enzyme in a cell is 0.01%. The protein content in a cell, exclusive of structural protein, is about 10% Hence, the cell could contain 10/0.01 or a 1,000 different enzymes if all this protein consists of enzymes. This figure is probably not too high, since we must remember that nearly every cellular reaction is catalyzed (see definition below) by a specific enzyme and there certainly must be a hundred known metabolic reactions for say, a liver cell." (2) Hundreds of different enzymes have been discovered, many even specific for the species of plant or animal in which they are found. Hundreds more undoubtedly await discovery by man, for the total number of enzymes has been estimated to be hundreds of thousands or even millions (2) For practically every organic compound which occurs in nature, there exists enzymes which bring about some type of reaction such as oxidation, reduction, hydrolysis, synthesis, etc.
Enzymes are responsible for the digestion and absorption of the food we eat, the breakdown (i.e., catabolism) of this food for energy and the building up (i.e., anabolism) of body proteins, carbohydrates, fats, hormones, and even enzymes themselves. Such diverse duties as the detoxification of harmful materials, the calcification of bone, the transportation of oxygen and carbon dioxide by the blood, and the clotting of blood are carried out by different enzymes. These hard workers labor in organized teams and as in a bucket brigade-one enzyme starts a reaction and passes the product to another enzyme which in turn modifies the product and so on down the line.
Enzymes have been defined as "catalysts of biological origin possessing a high molecular weight." (2) A catalyst is a substance which can change the rate of a chemical reaction without being modified as a result of that action. One might liken a catalyst to a mouse in a girls' dormitory, starting a reaction but not entering into it! Actually, an enzyme is believed to be modified in the course of a reaction but then to reappear in its original form after the reaction is completed. Molecular weights can range from about 13,000 to over 500,000, an extremely large and complex molecule (4). That all enzymes are protein in nature is generally accepted by all workers in the field but the actual structure of the molecules is very complex and still a mystery to man.
An enzyme functions by bringing about a reaction with a lower energy of activation than it would normally possess (2). The rate of a chemical reaction is proportional to the number of collisions of the participating molecules which in turn is dependent upon both concentration of the molecules and their activation (i.e., temperature). At the temperature and pH found in living substances, the rate of many reactions essential to life would be virtually nit without the aid of enzymes. A non-enzymatic duplication of the reactions which take place in nature often require extreme conditions of pH and/or temperature if they can be duplicated at all. Sometimes these extreme conditions cause such decomposition of the components that the reaction is impossible without enzymatic aid.
Michaelis and Menton (5) believe that an enzyme acts by forming a transient complex with the substrate (i.e., the substance being acted upon by the enzyme) and thereby changing the activation energy of the substrate so that a reaction can take place under biological conditions. For instance, at body temperature, enzymes enable glucose and fatty acids to be "burned" to carbon dioxide and water! Some enzymes are so efficient that one molecule is capable of transforming over a million molecules of substrate in one minute (9) !
In some enzymatic reactions there is little change in free energy, while others require energy (i.e., are endergonic) and still others supply energy (i.e., are exergonic). In biological systems these latter two types of reactions are often coupled; the endergonic reaction proceeding only if the ekergonic reaction takes place. Available energy for endergonic reactions may be in the form of a "storage battery," the high energy phosphate linkages found in adenosine triphosphate (ATP). Thus, when a reaction requires energy, it may "plug into" a phosphate linkage in ATP instead of an electrial outlet (6). When the phosphate linkage is disrupted, energy is released and this energy may eventually become apparent in the form of a heart beat, an inhalation or a muscular movement.
Some enzymes are composed only of protein, while others are proteins conjugated with a smaller molecule (i.e., prosthetic groups). These prosthetic groups are often vitamins (e.g., thiamine in the enzyme, cocarboxylase). In fact, the importance of many vitamins can be explained in terms of their direct participation in various enzymatic reactions. Some parts of the enzyme fholecule are essential for binding the enzyme to the substrate, some for changing the substrate molecule, while others are not at all essential for biological activity. For instance, pepsin will catalyze the hydrolysis of proteins even when all of the free amino groups of the enzyme molecule are blocked by acetylation, while even a very minor modification of other enzymes destroys their biological activity.
A very delicate system of checks and balances controls the action of enzymes in nature. Some enzymes in biological materials are present in the inactive form and must be converted into the active form before they can act upon a substrate. Enzymes can be activated by (a) the action of another enzyme (e.g., trypsinogen, the inactive form, is activated by enterokinase to form active trypsin, an enzyme which catabolyzes proteins in the small intestines) ; by (b) a change in pH (e.g., at a pH less than 5.2 pepsinogen, the inactive form, is changed to active pepsin, an enzyme that catabolyzes proteins in the stomach which has an acidity of about pH3) ; or by (c) metals (e.g., hexokinase, an enzyme which catabolyzes the breakdown of glucose requires the presence of magnesium). Enzymes can also be inhibited or inactivated by various substances. In such ways is the action of various enzymes controlled .
Many medicines as well as poisons, affect living organisms by their interference with enzymatic activity. For instance, some of the drugs which stimulate the action of the heart have also been shown to stimulate the action of cellular mitochondrial enzymes, while those drugs which depress the action of the heart also depress enzyme activity (6). Nerve gases affect living organisms by inhibiting the enzyme, cholinesterase. This enzyme is responsible for the hydrolysis of acetylcholine, a compound which is formed following a nerve impulse and which stimulates the contraction of the muscle. When cholinesterase is inhibited, the impulse continues unchecked and control of the muscle is lost. Indeed, it appears that many, if not most drugs and toxic materials affect living organisms by changing the action of enzymes.
There are many interesting facets to the discipline of enzymology, but perhaps the most fascinating of them all is the specificity which is exhibited by many enzymes. Inorganic catalysts are quite unspecific; for instance, nickel will catalyze the hydrogenation of a large number of substances. However, in nature, an enzyme usually acts upon only a very specific substrate or group of substrates. This specificity may be one of the following kinds: (a) The enzyme may be specific only for a certain type of chemical reaction; e.g., hydrolysis, reduction, oxidation, phosphorylation, etc., and therefore, of relatively low specificity, acting upon a rather large variety of substrates. (b) Other enzymes may be specific for certain classes of compounds; e.g., a proteinase will hydrolyze a protein but not a fat or carbohydrate. (c) Greater specificity is exhibited by an enzyme which will only break a bond in a specific position in the substrate molecule; e.g., exopeptidases hydrolyze only terminal peptide bonds of a protein while endopeptidases require neither free terminal amino nor carboxyl groups and, therefore, will split the protein molecule nearer the center. Pepsin and trypsin are of this latter type, but even these enzymes differ in that pepsin will break a peptide linkage involving an amino group of an aromatic amino acid while trypsin will break a peptide bond involving the amino acids, lysine or arginine (8). (d) The enzyme may be specific for a particular substrate; e.g., some carbohydrates will act only upon one specific glycosidic derivative of one of the many sugars found in nature. (e) The most exacting specificity, that of spacial arrangement, is exhibited by some enzymes. This requirement for a substrate of specific spacial configuration may be absolute, as in the case of D-amino acid oxidases which will oxidyze only an amino acid with the D- but not the L- configuration. These two types of compounds are identical in chemical properties and differ only in the fact that one is a mirror image (i.e., optical antipode) of the other!
Sometimes this spacial requirement is just relative, the enzyme reacting on one optical antipode faster than on the other. Fischer (7) likened an enzyme-substrate reaction to a key and a lock; they must fit perfectly in order to work.The action of some drugs can be understood in the
light of enzyme specificity. Antimetabolites, which include antibiotics, are so similar to a needed metabolite, which may well be a prosthetic group of some enzyme,
that the antimetabolite can act as an "imposter." An illustration of this can be shown in the case of sulfanilamide, an antimetabolite of para-amino benzoic acid (pABA), a vitamin which is probably a prosthetic group of an enzyme (8). The similarity of structure is evident from the formulae below:
In other words, sulfanilamide is similar enough to pABA to attach to the enzyme but dissimilar enough that the enzyme-prosthefic complex will not react as the normal complex reacts. To expand the analogy of the lock and the key, sulfanilamide fits into the keyhole, but can't turn the lock, and as long as it is in the keyhole, the normal key, pABA, cannot enter. In this manner, sulfanilamide evidently is antagonistic to bacteria which require pABA for existence. The relative concentrations of sulfanilimide and pABA must be considered in such antagonism, for one can "protect" the bacteria from sulfanilamide by an excess of PABA. In other words, the important thing is which one gets into the keyhole f irst. Other antibiotics, e.g. penicillin and Streptomycin, also appear to be antimetabolites but their mode of action is not yet clear (8).
Enzymes themselves have proven very useful as medicinal agents. Proteolytic enzymes are used for wound debridement (i.e., to rid a wound of dead tissue) and also as an aid to faulty gastrointestinal digestion. Streptokinase and streptodornase, two enzymes found in the streptococcus organism, have proved very efficient in digesting and liquifying pus, clotted blood and dead tissue which can accumulate in inflamed areas. Hyaluronidase or "spreading factor", is an enzyme useful in dentistry. This enzyme breaks down the "cement" between cells and allows fluids to diffuse through the tissues more rapidly. Now instead of the repeated injection of an anesthetic which was often necessary for a "direct hit" of the tiny nerve, the dentist can add this enzyme to enable the pain killer to spread rapidly to the nerve even if the needle is at some distance from the site. Enzymes also are useful in non-medical industries such as cheese, textile and leather industries to mention but a few (6).
Although these biological "workers" are employed by man, still further exploitation is possible. In fact the future of enzymology is even brighter than its past for so much concerning enzymes is still unknown. Not only the complete understanding of the action of vitamins, minerals, drugs, and toxic materials awaits discovery, but the study of enzyme activity, inhibition, and antagonism may well be the key to the control of one of man's most dreaded diseases, cancer.
In conclusion, should we not echo the Psalmist when he exclaimed "I will praise thee: for I am fearfully and wonderfully made: marvelous are thy works; and that my soul knoweth right well" (10) ? How can man even suggest that such a complicated system-so complicated that we are far from a thorough understanding of it - came into existence without the aid of a very superior being? Suggesting that this all came about from "lifeless" matter and that gradually this "lifeless" material, through the processes of evolution and without the direction of an intelligent being, became a form of "life" is virtually tantamount to suggesting that an intelligible novel would result from the combination of a dog, a typewriter and a pile of blank paper I
Unregenerate man continues to deny the Lord who made him when, now more than ever before, evidence Of his creative and sustaining power is at every hand!
(2) J. B. Sumner, G. F. Somers, Chemistry and Methods of Enzymes, 1947 Academy Press, New York, N.Y.(3) Ibid., 1953 edition.
(4) M. R_ Everett, Medical Biochemistry, 1946 Paul B. Hoeber, Inc., New York, N.Y.(5) Biochemische Zeitschrift 49:333 (1913).
(6) L. Galion, New Highways To Health, pg. 68 Nation's Business, March 1951.(7) Berichte der deutschen chemischen Geselischaft 27:2985
(8) E. A- West, W. P_ Todd, Textbook of Biochemistry, 1955 Macmillin and Son, Inc., New York, N.Y.
(9) J. S. Fniton, S. Simmonds, General Biochemistry, 1953 John Wiley and Son, Inc., New York, N.Y.(10) Psalin 139: 14.