Enzyme Kinetics in the Presence of an Inhibitor

The three most common types of inhibitors in enzymatic reactions are competitive, non-competitive, and uncompetitive. Competitive inliibition occurs when tlie substrate and inhibitor have similar molecules that compete for the identical site on the enzyme. Non-competitive inhibition results in enzymes containing at least two different types of sites. The inhibitor attaches to only one type of site and the substrate only to the other. Uncompetitive inhibition occurs when the inhibitor deactivates the enzyme substrate complex. The effect of an inhibitor is determined by measuring the enzyme velocity at various 

A more reliable determination of K is achieved if the observed is determined at various concentrations of inhibitor. Each curve is then fitted to determine the observed K ,. The inhibitor is entered as the 

Competitive and non-eompetitive inhibitions are easily distinguishable from the Lineweaver-Burk plot. In the ease of eompetitive inhibitors, the intereept on tlie 1/Cg axis inereases while tlie intereept of tlie 1/v axis remains unehanged by the addition of the inhibitor. Conversely, with a non-eompetitive inhibitor, only the 1/v axis intereept inereases. The effeet of eompetitive inhibitors ean be reversed by inereasing the substrate eoneentration. Where the enzyme or the enzyme substrate eomplex is made inaetive, a non-eompetitive inhibitor deereases of the enzyme, but remains eonstant. 

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