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Enzymes

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File:Enzyme action.png
Muessig/CC/Wikimedia Commons
Definition:

Enzymes are proteins that participate in cellular metabolic processes with the ability to enhance the rate of reaction between biomolecules. Some enzymes can even reverse a reaction from the direction it would normally take, by reducing the activation energy (Ea) to the extent that the reaction favours the reverse direction. Simlarly, enzymes can catalyze reactions that might not otherwise occur, by lowering the Ea to a more "affordable" level for the cell.

Enzymes can be isolated using various protein purification methods. The purity of an enzyme preparation is measured by determining it's specific activity

Enzyme Composition

Enzymes can have molecular weights ranging from about 10,000 to over 1 million. A small number of enzymes are not proteins, but consist of small catalytic RNA molecules. Often, enzymes are multiprotein complexes made up of a number of individual protein subunits.

Many enzymes catalyze reactions without help, but some require an additional non-protein component called a co-factor. Co-factors may be inorganic ions such as Fe2+, Mg2+, Mn2+, or Zn2+, or consist of organic or metalloorganic molecules knowns as co-enzymes.

Enzyme Classifications

Enzymes are classified according to the reactions they catalyze. The six classes are:

  1. Oxidoreductases
  2. Transferases
  3. Hydrolases
  4. Lyases
  5. Isomerases
  6. Ligases
Examples:
  1. Alcohol dehydrogenase: an oxidoreductase converting alcohols to aldehydes/ ketones.
  2. Aminotransferases: transferases catalyzing the amino acid degradation by removing amino groups.
  3. Glucose-6-phosphatase: a hydrolase that removes the phosphate group from glucose-6-phosphate, leaving glucose and H3PO4.
  4. Pyruvate decarboxylase: a lyase that removes CO2 from pyruvate.
  5. Ribulose phosphate epimerase: an isomerase that catalyzes the interconversion of ribulose-5-phosphate and xylulose-5-phosphate.
  6. Hexokinase: a ligase that catalyzes the interconversion of glucose and ATP with glucose-6-phosphate and ADP.

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