Idézet:

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Types

Homotropic

A homotropic allosteric modulator is a substrate for its target protein, as well as a regulatory molecule of the protein's activity. It is typically an activator of the protein.[1] For example, O2 and CO are homeotropic allosteric modulators of hemoglobin. Likewise, in IMP/GMP specific 5' nucleotidase, binding of one GMP molecule to a single subunit of the tetrameric enzyme leads to increased affinity for GMP by the subsequent subunits as revealed by sigmoidal substrate versus velocity plots.[1]

Heterotropic

A heterotropic allosteric modulator is a regulatory molecule that is not the enzyme's substrate. It may be either an activator or an inhibitor of the enzyme. For example, H+, CO2, and 2,3-bisphosphoglycerate are heterotropic allosteric modulators of hemoglobin.[12] Once again, in IMP/GMP specific 5' nucleotidase, binding of GTP molecule at the dimer interface in the tetrameric enzyme leads to increased affinity for substrate GMP at the active site indicating towards K-type heterotropic allosteric activation.[1]
As has been amply highlighted above, some allosteric proteins can be regulated by both their substrates and other molecules. Such proteins are capable of both homotropic and heterotropic interactions.[1]

Essential activators

Some allosteric activators are referred to as "essential", or "obligate" activators, in the sense that in their absence, the activity of their target enzyme activity is very low or negligible, as is the case with N-acetylglutamate's activity on carbamoyl phosphate synthetase I, for example.[13][14]

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