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Hexokinase-I (HK-I) is an enzyme activator because it draws glucose into the glycolysis pathway. Its 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.
Inhibitor binding to this allosteric site changes the conformation (that is, the tertiary structure or three-dimensional shape) of the enzyme so that the affinity of the substrate for the active site is reduced. [22]
"INHIBITORS, INDUCERS AND SUBSTRATES OF CYTOCHROME P450 ISOZYMES". "The Life Raft Group: Long List of Inhibitors and Inducers of CYP3A4 and CYP2D6". "DRUGBANK Online: Cytochrome P-450 Enzyme Inhibitors". "MEDICATIONS METABOLIZED BY CYTOCHROME P450 3A4" (PDF)
A transcriptional activator is a protein (transcription factor) that increases transcription of a gene or set of genes. [1] Activators are considered to have positive control over gene expression, as they function to promote gene transcription and, in some cases, are required for the transcription of genes to occur.
Plasminogen activator inhibitor-1 is a serine protease, synthesized by endothelial cells, that specifically inhibits tissue plasminogen activator (tPA) and urokinase (uPA). Tissue plasminogen activator and urokinase are the activators of plasminogen and result in the breakdown of blood clots (fibrinolysis). [4]
Similarly, inhibitors such as ATP and PEP bind to the same allosteric site and facilitate the formation of the T state, thereby inhibiting enzyme activity. The hydroxyl oxygen of carbon 1 does a nucleophilic attack on the beta phosphate of ATP. These electrons are pushed to the anhydride oxygen between the beta and gamma phosphates of ATP. [10 ...
However, when present in a high enough concentration to counteract the effects of plasminogen activator inhibitor, tPA can bind plasminogen, cleaving off the bound plasmin from it. Plasmin, another type of protease, can either be bound by a plasmin inhibitor, or work to degrade fibrin clots, which is the main therapeutic pathway. [37]
Non-competitive inhibition models a system where the inhibitor and the substrate may both be bound to the enzyme at any given time. When both the substrate and the inhibitor are bound, the enzyme-substrate-inhibitor complex cannot form product and can only be converted back to the enzyme-substrate complex or the enzyme-inhibitor complex.