3.11 : Introduction to Enzymes

The use of enzymes by humans dates to 7000 BCE. Humans first used enzymes to ferment sugars and produce alcohol without knowing that this was an enzyme-catalyzed reaction. Wilhelm Kuhne coined the term 'enzyme' in 1877 from the Greek words ‘en’ meaning ‘in’ or ‘within’ and ‘zyme’ meaning ‘yeast.’

Most enzymes are proteins that speed up biochemical reactions without being consumed. Enzymes contain one or more active sites that bind the substrates and convert them into products. Many enzymes also have allosteric sites, additional sites where molecules other than substrates bind to activate or inhibit the enzyme.

Some enzymes require the presence of cofactors– metal ions or organic molecules for catalysis. Cofactors bind to the active site of an enzyme and assist in the conversion of substrates into products. An enzyme without a cofactor is an apoenzyme and becomes a holoenzyme once it binds a cofactor. A cofactor that is an organic molecule is called a coenzyme. Most coenzymes are vitamin-derived.

Inhibitors are molecules that stop an enzyme-catalyzed reaction. Competitive inhibitors are similar to substrate molecules and compete with them to bind to the active sites. In contrast, non-competitive inhibitors bind to allosteric sites and change the enzyme conformation to reduce substrate binding.