Enzyme

An enzyme is a biological macromolecule that acts as a biological catalyst. Most enzymes are proteins that speed up chemical reactions without being consumed during the process. These reactions are essential for life because nearly all metabolic processes in a cell depend on enzyme catalysis to occur at biologically relevant rates. A metabolic pathway is often a series of these enzyme-catalyzed steps working in a sequence.

Without these helpers, the chemical processes required for life would happen much too slowly. Enzymes increase reaction rates by lowering the activation energy, which is the energy required to start a reaction. This can increase speed by factors of millions. For example, the enzyme orotidine 5′-phosphate decarboxylase accelerates a reaction that would otherwise take millions of years to occur in just milliseconds.

To understand how they work, we must look at their complex three-dimensional structure.

Enzymes are usually globular proteins, meaning they are shaped like rounded balls. The specific sequence of amino acids determines this shape, and the shape determines the function. Most enzymes are much larger than the molecules they act upon, which are called substrates. A small portion of the enzyme, usually only two to four amino acids, is directly involved in the chemical work. This area is called the catalytic site. The catalytic site is located next to binding sites that orient the substrates correctly. Together, the catalytic site and the binding sites form the active site.

Some enzymes also have allosteric sites, where a small molecule can bind to change the enzyme's shape and adjust its activity.

Enzymes are highly specific, meaning they usually only work with certain substrates. This specificity is determined by their unique shape. However, enzymes are also sensitive to their environment, particularly temperature and pH levels.

As temperature increases, enzyme activity typically increases due to the Q10 coefficient. If the temperature becomes too high, the enzyme may undergo denaturation. Denaturation is when the enzyme loses its structure and unfolds, leading to a loss of function. This is why enzymes from bacteria in volcanic hot springs are so valuable to industry; they can function at very high temperatures without denaturing. While most enzymes are proteins, there are other types of biocatalysts. Ribozymes are catalytic RNA molecules, such as the components found in a ribosome. Recently, scientists have also identified biomolecular condensates as a third category of biocatalysts.

Scientists use specific systems to classify and name these molecules.

One method is to classify them by their enzymatic activity using the Enzyme Commission, or EC, numbering system. An enzyme is fully specified by four numbers. The first number identifies the broad class of reaction. For example, EC 1 represents Oxidoreductases, which handle oxidation-reduction reactions. EC 2 are Transferases, which move functional groups. EC 3 are Hydrolases, which use water to break bonds. EC 4 are Lyases, EC 5 are Isomerases, EC 6 are Ligases, and EC 7 are Translocases. Another way to classify enzymes is by sequence similarity, grouping them into families based on their amino acid patterns. Interestingly, unrelated enzymes can sometimes perform the same reaction; these are called non-homologous isofunctional enzymes.

The history of enzymology reveals how our understanding of life has evolved.

In the late 17th and early 18th centuries, people knew meat digested in the stomach, but they did not know how. In 1833, French chemist Anselme Payen discovered the first enzyme, called diastase. Later, Louis Pasteur studied yeast fermentation and believed it was caused by a "vital force" inside living cells. In 1877, German physiologist Wilhelm Kühne coined the term "enzyme" to describe these processes. This changed when Eduard Buchner showed in 1897 that yeast extracts could cause fermentation without living cells. He discovered the enzyme zymase and later won the Nobel Prize in 1907. The practice of naming enzymes with the suffix "-ase" is traced to Émile Duclaux.

For a long time, scientists debated whether enzymes were actually proteins. In the early 1900s, some argued that proteins were just carriers for the real enzymes. This was settled in 1926 when James B. Sumner showed that the enzyme urease was a pure protein. Later, John Howard Northrop and Wendell Meredith Stanley proved this by working with digestive enzymes like pepsin and trypsin. Their work earned them a Nobel Prize in 1946. Once scientists learned how to crystallize enzymes, they could use x-ray crystallography to see their structures. In 1965, the structure of lysozyme was published, which helped start the field of structural biology. This allowed researchers to see how enzymes work at an atomic level.

Today, enzymes have many practical uses in industry and daily life. In manufacturing, they are used to produce antibiotics and other complex molecules. In your home, enzymes in biological washing powders help break down stains made of protein, starch, or fat. In the food industry, proteolytic enzymes like papain are used as meat tenderizers to improve texture. Because enzymes are regenerated at the end of every cycle and are not consumed, they are incredibly efficient tools for both nature and human technology.