Enzymes with two sites are called [AIIMS 2002]
Allosteric enzyme
Allosteric enzymes are enzymes that change their conformational ensemble when they bind with an effector. This results in an apparent change in binding affinity at a different ligand binding site.
These enzymes have multiple protein subunits. Ligands that bind to allosteric enzymes and affect binding at a different site on the enzyme are known as effectors.