The K_m of an enzyme is always decreased by which class of inhibitor?

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11ecba2d_0f14_5cbf_a3bf_1d46eb0d31e8_MD0008_00 Enzyme inhibitors are classified according to the mechanism by which they interfere with enzyme activity. Competitive inhibitors bind the free enzyme E exclusively and prevent substrate from binding. Uncompetitive inhibitors bind the enzyme-substrate complex ES exclusively, preventing the enzyme from converting substrate to product. Mixed inhibitors have characteristics of both competitive and uncompetitive inhibitors. All mixed inhibitors bind both E and ES but may favor one over the other. When a mixed inhibitor binds E and ES with equal affinity, it is a noncompetitive inhibitor. Different inhibitory mechanisms have different effects on an enzyme's properties. Specifically, inhibitor binding to E prevents substrate binding, so a higher substrate concentration is required to reach ½V_max. This substrate concentration is the K_m of the enzyme, so competitive inhibitors always cause an increased K_m (Choice C). Conversely, inhibitor binding to ES effectively decreases the amount of ES in solution and shifts the equilibrium toward more ES formation. This causes a decrease in the amount of substrate needed to achieve ½V_max (although V_max itself is also decreased) and therefore decreases K_m. Because uncompetitive inhibitors bind ES exclusively, they always cause a decrease in K_m. (Choices A and B) Mixed inhibitors may cause a decrease, increase, or no change in K_m, depending on whether they favor binding to E (increased K_m) or ES (decreased K_m). If the mixed inhibitor has equal affinity for E and ES, it is noncompetitive and does not alter K_m. Educational objective: Enzyme inhibitors are classified by their mechanism of action. Inhibitors that bind free enzyme E exclusively are competitive inhibitors and cause an increased K_m. In contrast, inhibitors that bind enzyme-substrate ES complex exclusively are uncompetitive and cause a decreased K_m. Mixed inhibitors have characteristics of both uncompetitive and competitive inhibitors, and may cause an increase, decrease, or no change (ie, noncompetitive inhibitors) in K_m, depending on whether they favor binding to E or ES.

The Km of an Enzyme Is Always Decreased by Which

The K_m of an Enzyme Is Always Decreased by Which