Acompetitive inhibitor of an enzyme-catalyzed reaction - cannot bind to the active site. - always interferes with product release. - is usually structurally similar to the substrate. - binds to an allosteric site. - inhibits to the same extent at all substrate concentrations.

is usually structurally similar to the substrate.

Explanation:

Competitive inhibitors resemble normal substrate and binds to enzyme at the active site usually and prevents substrate from binding.

Active sites are main location for the substrate-enzyme binding. These sites involve weak as well as reversible bonds between the substrate and the enzyme. These inhibitors bind to the active sites and form weak and  reversible bonds. Competitive inhibitors can be dissociated from active site by increasing concentration of the substrates. Substrates has to compete for active site and displace the bound competitive inhibitors.

Hence, correct option is - is usually structurally similar to the substrate.

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