Black-eyed beans are a source of B vitamins

Cunning catalysts

Enzymes are proteins

Enzymes, like inorganic chemical catalysts, cannot make new reactions happen, but they speed them up enormously by lowering the activation energy for the reaction.

Generally, enzymes are globular proteins, and they need the right conditions to do their job. Substrate–enzyme binding often depends on weak electrostatic forces and is easily disrupted by changes in acidity (pH). Heat denatures proteins and destroys enzyme activity.

Competitive inhibitors are molecules that have a similar shape to the enzyme’s substrate, but do not react and instead block the active site. These competitive inhibitors can make good drugs – and poisons.

Many enzymes need a non-protein component called a cofactor to work. Some contain a metal atom held inside a stable chemical structure, such as haem in cytochrome 450, an enzyme that detoxifies chemicals in the liver. This is why we need traces of metals such as iron, magnesium, copper and zinc in our diet. Organic cofactors, known as coenzymes, often come from vitamins and make up part of the enzyme’s active site. NAD is an example of a cofactor, derived from niacin (vitamin B3).

Lead image:

Black-eyed beans are a good source of B vitamins, including thiamin, niacin and riboflavin.

iStockphoto

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About this resource

This resource was first published in ‘Proteins’ in January 2014.

Topics:
Cell biology, Biotechnology and engineering
Issue:
Proteins
Education levels:
16–19, Continuing professional development