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Enzyme activator

Enzyme activators are molecules that bind to enzymes and increase their activity. They are the opposite of enzyme inhibitors. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism. An example of an enzyme activator working in this way is fructose 2,6-bisphosphate, which activates phosphofructokinase 1 and increases the rate of glycolysis in response to the hormone insulin. In some cases, when a substrate binds to one catalytic subunit of an enzyme, this can trigger an increase in the substrate affinity as well as catalytic activity in the enzyme's other subunits, and thus the substrate acts as an activator.

Examples of enzyme activator:

Hexokinase-I (HK-I) is an enzyme activator because it draws glucose into the glycolysis pathway. It's function is to phosphorylate glucose releasing glucose-6-phosphate (G6P) as the product. HK-I not only signals the activation of glucose into glycolysis, but also maintains a low glucose concentration to facilitate glucose diffusion into the cell. It has two catalytic domains (N-terminal domain and C-terminal domain) which are connected through a α-helix. The N-terminal acts as an allosteric regulator of C-terminal; the C-teminal is the only one involved in the catalytic activity. HK-I is regulated by the concentration of G6P, where G6P acts as a feedback inhibitor. At low G6P concentration, HK-I is activated; at high G6P concentration the HK-I is inhibited.