Regulation of Enzyme Activity

Regulation of Enzyme Activity - Regulation of Enzyme...

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Regulation of Enzyme Activity. Genetic Regulation determines whether or not the gene for an enzyme is expressed and the enzyme is produced. Allosterism is a method of regulating enzymes by using natural inhibitors in cells. Allosterism mimics non-competitive inhibition. For example, PFK is one of the key enzymes in terms of regulation of glycolysis. PFK converts Fructose-6-Phosphate into Fructose-1,6- bisphosphate. PFK is inhibited by Fructose-1,6-bisphosphate, ATP, and citric acid. A dynamic equilibrium results from the feedback inhibition. The regulation is finely attuned to a wide range of ATP concentrations; at increased concentrations of ATP, most enzymes are inactivated via negative feedback. Covalent Modification is another method of regulating enzyme activity. The presence or absence of covalent modification determines whether an enzyme is active or inactive. The most common method of covalent modification is phosphorylation. Kinases are any enzyme that adds a Phosphate group to another compound. Protein kinases phosphorylate hydroxyl groups of serine, threonine, and typtophan molecules of an enzyme’s amino acid sequences. The introduction of a bulky phosphate group alters an enzyme’s three-dimensional conformation, which thus alters the activity status of that enzyme. Another example of gene regulation by covalent modification is the regulation of glycogen phosphorylase activity. The regulation is part of an enzyme cascade; cascades are multi-step processes which amplify an initial weak signal into a greater response. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide. Many proteins are glycosylated via glycosidic bonds. The function of glyco groups is not well understood. One possibility is that they serve to protect against proteolysis; some glyco groups provide viscosity and serve as natural antifreeze in Antarctic fish. Disaccharide provides H-bonds to the surrounding water molecules and prevents the formation of ice crystals and freezing. Know that there is cell-to-cell recognition present. Zymogens are inactive enzyme precursors. Zymogens are activated by proteolytic cleavage; which means that they need to be cut by a protease. Pro-insulin is inactive, but all it takes is a protease to react to the state of metabolic conditions to clip amino acids from pro-insulin. The result is two different chains of the original molecule, still held together by its disulfide bridges. Chymotrypsinogen is a digestive protease. It is not active when first made. However, it is cleaved by trypsin and converted to chymotrypsin.
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  • Fall '08
  • Enzyme

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