-Occurs when the inhibitor has a similar molecular configuration as the normal substrate (i.e its shape resembles the enzyme’s normal substrate).
-Consequently the inhibitor competes with the normal substrate to occupy the active site
-It prevent the enzymes from combining with the normal substrate and the reaction the not proceed.
-The degree of inhibition depends on the concentration of the substrate and inhibitor, a high concentration of inhibitor compared to that of the substrate slows down the reaction.
-The effect of inhibition may also depend on how tightly the enzyme binds to the inhibitor and substrate.
-Examples: malonic acid which binds the enzyme succinic dehydrogenase.