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Adding a competitive inhibitor to an enzymatic reaction increases the K m of the reaction, but the V max remains the same. Sulfa drugs also act as competitive inhibitors. For example, sulfanilamide competitively binds to the enzyme in the dihydropteroate synthase (DHPS) active site by mimicking the substrate para-aminobenzoic acid (PABA). [15]
An inhibitor can reduce the effectiveness of a catalyst in a catalysed reaction (either a non-biological catalyst or an enzyme).E.g., if a compound is so similar to (one of) the reactants that it can bind to the active site of a catalyst but does not undergo a catalytic reaction then that catalyst molecule cannot perform its job because the active site is occupied.
An example of such a transition state inhibitor is the antiviral drug oseltamivir; this drug mimics the planar nature of the ring oxonium ion in the reaction of the viral enzyme neuraminidase. [ 47 ] However, not all inhibitors are based on the structures of substrates.
Disulfiram is a medication used to support the treatment of chronic alcoholism by producing an acute sensitivity to ethanol (drinking alcohol). Disulfiram works by inhibiting the enzyme aldehyde dehydrogenase (specifically the ALDH2 enzyme [3]), causing many of the effects of a hangover to be felt immediately following alcohol consumption.
In enzyme-catalyzed reactions, the overall activation energy of the reaction is lowered when an enzyme stabilizes a high energy transition state intermediate. Transition state analogs mimic this high energy intermediate but do not undergo a catalyzed chemical reaction and can therefore bind much stronger to an enzyme than simple substrate or ...
Other examples of drugs dependent on CYP3A4 for their metabolism are escitalopram, [45] warfarin, [46] oxycodone, tramadol, and oxymorphone. The concentrations of these drugs may increase if they are used concomitantly with omeprazole. [47] Omeprazole is also a competitive inhibitor of p-glycoprotein, as are other PPIs. [48]
A number of drugs do not cause disulfiram-like reactions, but have other unintended interactions with alcoholic drinks. For example, alcohol interferes with the efficacy of erythromycin. Patients on linezolid and tedizolid may be sensitive to the tyramine present in tap beers and red wine. [8]
Substrate analogs (substrate state analogues), are chemical compounds with a chemical structure that resemble the substrate molecule in an enzyme-catalyzed chemical reaction. Substrate analogs can act as competitive inhibitors of an enzymatic reaction. An example is phosphoramidate to the Tetrahymena group I ribozyme. [1]