Enzymes have been called the "agents of life" because all life processes are dependent on them. Enzymes are protein molecules that act as catalysts (they speed up chemical reactions without undergoing any change themselves). They can build up or break down other molecules and are responsible for regulating the many chemical reactions that occur in plants and animals. If enzymes were absent from the human body, most of its metabolic reactions would occur at a rate, too slow to support life.

Enzymes accelerate reactions by at least a million times. Molecules in the cells of solid tissues and in circulating blood are constantly being split apart and welded together again by enzymatic action. It has been estimated that a single cell, roughly one-billionth the size of a drop of water, contains about 3,000 different enzymes.

Regulatory Functions

In addition to speeding up reactions, enzymes also have regulatory functions. It is essential that chemical reactions inside cells are controlled so that they do not make too little or too much of a particular product. Many of the processes, or pathways, in cells must be coordinated, and this is a function enzymes regulate. Enzymes are thus central not only to individual reactions within a cell but also to the life of the cell as a whole.

Enzymes are critical to the proper functioning of everything from breathing to thinking to blood circulation to digestion. They can be broken down into two major groups, metabolic enzymes and digestive enzymes. Metabolic enzymes are produced by the body to regulate functions in the blood, tissues, and organs. Digestive enzymes are produced to break down food and absorb nutrients.

Enzymes and Digestion

Prior to the eighteenth century, the process of digestion was believed to be solely a mechanical process, similar to a meat grinder. In 1752, however, French scientist Rene-Antoine Reaumur fed his pet falcon pieces of meat enclosed in a metal tube with holes in it. He wanted to protect the meat from the mechanical effects of the bird's stomach friction. When he removed the tube a few hours later, the meat had been digested, but the tube was still intact. It was evident that the digestion had resulted from chemical, not mechanical, action. In the 1780s Italian biologist Lazzaro Spallanzani also proved that meat could be digested by gastric juices extracted from falcons. His was probably the first experiment in which a vital reaction occurred outside the living organism.

John R. Young, who graduated from the University of Pennsylvania in 1803, added to the increasing knowledge about digestion. In his graduation essay, he described his experiments on frogs and snakes and on himself. He was the first researcher to reveal that gastric juice contains a strong acid. Young believed that the strong acidity of gastric juice was responsible for its digestive action. In 1835, however, German physiologist Theodor Schwann discovered that gastric juice also contained a non-acid digestive substance. He called the substance pepsin (from the Greek for "to digest"), which was later shown to be an enzyme.


The oldest known enzyme reaction is alcoholic fermentation, which was thought to be a spontaneous reaction until Louis Pasteur (1822—1895) proved otherwise in 1857. Pasteur found that fermentation was caused by yeast cells digesting sugar for their own nourishment. In 1878 German physiologist Wilhelm Kuhne (1837-1900) coined the term "enzyme," meaning "in leaven," to describe this process. The word enzyme was used later to refer to substances such as pepsin, and the word ferment was used to refer to chemical activity produced by living organisms.

In 1897 another German scientist, Eduard Buchner, discovered by accident that fermentation actually does not require the presence of living yeast cells. Buchner made an extract of yeast cells by grinding them and filtering off the remaining cell debris. Then he added a preservative—sugar—to the resulting cell-free solution to preserve it for future study. He observed that fermentation, the formation of alcohol from sugar, occurred. Buchner then realized that living cells were not required for carrying out metabolic processes such as fermentation. Instead, there must be some small entities capable of converting sugar to alcohol. These entities were enzymes. Buchner's accidental discovery won him the 1907 Nobel Prize in chemistry.

After Buchner's discovery, most scientists assumed that fermentation and other metabolic reactions were caused by enzymes. All attempts to isolate and determine the chemical nature of enzymes were unsuccessful, however, until 1926. That year American biochemist James Sumner of Cornell University isolated the enzyme urease from the jackbean after nine years of research. The enzymes pepsin and trypsin were isolated four years later by the American biochemist John H. Northrop. It was later shown that enzymes are proteins. In more recent research, ribonuclease, a three-dimensional enzyme, was discovered in 1938 by the American bacteriologist Ren6 Dubos. The enzyme was synthesized by American researchers in 1969.

Enzymes in Medicine

Some diseases can be treated by using substances that inhibit (curb) enzymes. Inhibitors can be used to attack enzymes that are critical to the survival of an organism when such undesirable organisms as disease-causing bacteria or parasites pose a threat to health. Neostigmine, used to treat myasthenia gravis (a disease that causes severe muscle weakness), strongly inhibits the enzyme cholinesterase. L-asparaginase is believed to be a potent weapon for treating leukemia. And a class of enzymes called dextrinases are believed to be effective in preventing tooth decay.

Research is also being conducted into malfunctioning of enzymes, which may be linked to such blood disorders as diabetes and anemia. Geneticists have also discovered that in some hereditary diseases, such as phenylketonuria and galactosemia, the affected individuals are actually missing certain enzymes. Some of these enzyme-deficiency diseases can now be effectively treated, and many researchers are concentrating on the search for more of these disorders, which may ultimately revolutionize the practice of medicine.

[See also Genetic engineering ]

User Contributions:

does anyone know how individual cells get nutrients?
i need more fact on the role of enzymes on fermentation,and more resent
i think enzymes are the speeders of all known biological processes. i think i really need to know their origin
Omsakash Agrawal
We are using few green leaves powder(dehydrated below 45degree C.) for preventive & curative measure & geting good response
amabo sonia
i need to know more on the effects of excess enzymes to the body health
My son had a cardiac event during eye surgery several years ago & needed life support to save him. We were told the adverse reaction he had was a 1-9 million chance. Before this event he had no health problems & no allergies. ( It was an eye surgery to correct his vision)He has a missing enzyme in his blood & we are now having serious problems with him & sphyciatric meds he takes for bipolar. This missing enzyme has never been identified & now we need to identify it. Any ideas which 1 it would be?

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