Enzyme

An enzyme is a biological molecule that serves as a catalyst for chemical reactions. In these reactions, molecules are converted from substrates to products. Enzymes are required for most chemical reactions in the cells of living organisms, called biological cells. These reactions, in turn, are necessary to sustain life. Enzymes select the substrates they will use to speed up reactions.

Their role in the body

Enzymes are found in every organ, and in every cell, in the body. This includes the blood, intestinal fluids, saliva and the stomach.

They are also integral to all bodily functions. Some examples of enzymes at work include the body breaking down food — with both saliva and gastric juice — and blood clotting.

Mechanism of action

The mechanism of action is that enzymes lower the activation energy for a reaction; namely, the enzyme reduces the amount of energy necessary to carry out the reaction, thereby allowing it to occur at an increased rate, often at rates millions of times faster than comparable reactions that are un-catalyzed. Once these reactions occur, equilibrium is reached. Enzymes are not consumed during the reaction, and they do not alter the equilibrium state reached by those reactions.

About 4,000 biochemical reactions are catalyzed by enzymes. There are many possible substrates from which to choose, but each enzyme or set of enzymes in a cell determines which metabolic pathways occur in that particular cell. A metabolic pathway is when one enzyme takes the product of another enzyme as a substrate. The product of that reaction is then taken by another enzyme as a substrate. Sometimes, the same enzyme will catalyze multiple reactions in the chain.

Enzymes often serve in the digestive systems of living organisms. Amylases and proteases are enzymes that break down large molecules — including starches or proteins — into smaller molecules. The smaller molecules may then be absorbed by the intestines. Starch molecules are turned into maltose or glucose

Malfunctions of enzymes

Malfunctioning of enzymes, including mutation, overproduction, under-production or deletion, may lead to genetic diseases such as phenylketonuria, pseudocholinesterase and certain forms of cancers. Conversely, oral administration of enzymes may be used to treat diseases such as pancreatic insufficiency and lactose intolerance. Artificial enzymes that catalyze reactions in an enzyme-like way have been synthesized and used to treat various conditions.

Drugs to treat diseases such as influenza and HIV use enzyme inhibitors to stop reactions that contribute to the disease process.

Additional information may be found at these websites:

http://bloodjournal.hematologylibrary.org/cgi/collection/gene_expression

http://www.nlm.nih.gov/medlineplus/ency/article/003706.htm

http://www.mayoclinic.com/health/metabolism/WT00006/

http://www.nature.com/jcbfm/index.html

http://www.nutritionandmetabolism.com/

http://www.hormone.org/Public/endocrinologist.cfm

http://www.nlm.nih.gov/medlineplus/ency/article/002257.htm

http://www.ncbi.nlm.nih.gov/books/NBK22/?depth=10

http://endo.endojournals.org/

http://www.mayoclinic.org/medicalprofs/glucocorticoid-induced-diabetes.html