Allosteric inhibitors do not compete for the active sites in enzymes. Why?
Allosteric inhibitors are a type of non-competitive inhibitors because they do not bind to the active sites of the enzymes. The structure of allosteric inhibitors are not similar to the substrate but may be similar to one of the cofactors or coezymes. They bind to a site other than the active site and block enzyme activity either by steric hindrance or by modifying the active sites such that it is not available for the substrates.
Competitive inhibitors have a structure similar to the enzyme substrate and they compete with the substrates for the active sites of the enzymes.