What are Enzymes?
Have you ever read a biology journal? If you have, of course you will find enzymes and their explanations. Enzymes are biocatalysts for biochemical reactions in living organisms.
A biocatalyst is a biological substance that can speed up a biochemical reaction without being consumed in the biochemical reaction. In an enzymatic reaction, the enzyme converts the initial molecule of the substance, the substrate, into a reaction product whose molecular shape is different from the initial molecule. The molecules resulting from this reaction are called products.
Almost every reaction in a biological cell requires enzymes in order to occur at a significant rate. Enzymes only react with certain substrates (work specifically) and only catalyze certain reactions. The action of specific enzymes determines what reactions and how they occur in the cell. The sequence of reactions that occur in these cells is called the metabolic pathway.
Enzyme activity can be influenced by other molecules. Molecules that decrease enzyme activity are called inhibitors. Most drugs and poisons are inhibitors. Molecules that increase enzyme activity are called activators. Enzyme activity is also affected by temperature, substrate concentration and environmental conditions, such as acidity.
History of Enzymes
Enzymes are very close to the daily life of humans. Digestion of meat in the stomach, conversion of starch into simple sugars in our mouth, and so on.
However, the word enzyme was only used by Wilhelm Kuhne in 1877. Kuhne used the Greek (read: enzyme) which means 'in yeast'. This word was used in Kuhne's attempt to describe the substances involved in alcoholic fermentation.
The word enzyme now refers only to non-biological substances, such as pepsin, while the word fermentation refers to the chemical activity produced by living organisms.
Eduard Buchner, in 1897, discovered that enzymes could work outside living cells. James B. Sumner, in 1926, succeeded in showing that the enzyme urease is a pure protein and successfully crystallized it.
Northrop and Stanley provided definitive evidence through their research on the enzymes pepsin, trypsin, and chymotrypsin.
Structure and Mechanism of Enzyme Action
Enzymes are generally globular proteins consisting of at least 62 amino acids. Enzyme activity is determined by its three-dimensional structure. However, until now, the problem of how the three-dimensional structure of enzymes can affect enzyme function remains unsolved.
Most enzymes are much larger than their substrates and only a small fraction of the enzymes (between three and four amino acids) are directly involved in the catalysis process. The part of the enzyme that contains the catalytic residue, binds to the substrate, and which causes the reaction to occur is known as the active site.
Enzymes can also have sites that bind to cofactors. Cofactors are parts of enzymes that are not proteins but are important in inactivating enzymes. Enzymes that do not have cofactors are inactive and are called apoenzymes. While enzymes that have cofactors, are called holoenzymes.
Cofactors can be inorganic compounds (such as metal ions or iron-sulfur groups) or organic compounds (such as flavins and heme). Organic cofactors can be in the form of a prosthetic group that is strongly bound to the enzyme or in the form of a coenzyme that is weakly bound to the enzyme. Coenzymes are released from enzymes during reactions.
So, how do enzymes work? Emil Fisher describes how enzymes work with a key and lock model. So, like a lock that can only be opened by a special key. Likewise, enzymes that only react with certain substrates. This indicates that the enzyme is working specifically.