Enzyme

An enzyme (from Greek énsimo (??????), formed by én = at or in and simo = leaven or yeast) is a protein that catalyzes, or speeds up, a chemical reaction.

Metabolic pathways and allosteric enzymes

Several enzymes can work together in a specific order, creating metabolic pathways. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme. The end product(s) of such a pathway are often inhibitors for one of the first enzymes of the pathway (usually the first irreversible step, called committed step), thus regulating the amount of end product made by the

Related Topics:
Metabolic pathway - Inhibitors

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pathways. Such a regulatory mechanism is called a negative feedback mechanism, because the amount of the end product produced is regulated by its own concentration. Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps with effective allocations of materials and energy economy, and it prevents the excess manufacture of end products. Like other homeostatic devices, the control of enzymatic action helps to maintain a stable internal environment in living organisms.

Related Topics:
Negative feedback mechanism - Homeostatic devices

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Enzymes that are regulated by end-production inhibition are usually allosteric enzymes. An allosteric enzyme molecule has an active site and also an allosteric site. The allosteric site can bind with allosteric effectors that affect the activity of the enzyme molecule. Allosteric effectors include allosteric activators and allosteric inhibitors. The binding with an allosteric activator activates an enzyme molecule because the active site is in the right conformation to bind with substrate molecules. The binding with an allosteric inhibitor inactivates the enzyme molecule because the conformation of the active site is altered. The activation and inhibition of an allosteric enzyme are reversible.

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