allosterisk

Allosterisk (allosteric in English) refers to regulation of a protein's activity through binding of a ligand at a site distinct from the active site, called the allosteric site. Allosteric proteins are often oligomeric, with multiple subunits and multiple active sites, and ligand binding induces conformational changes that alter activity at one or more active sites.

Effector molecules can be positive (activators) or negative (inhibitors). Allostery enables feedback control of metabolic pathways and rapid responses to cellular conditions. Two classical frameworks describe allostery: the concerted model (Monod–Wyman–Changeux) in which all subunits switch between conformations in a coordinated fashion, and the sequential model (KNF) in which ligand binding induces progressive conformational changes in neighboring subunits or sites.

Allosteric regulation can occur by small metabolites, nucleotides, metal ions, or through post-translational modifications that alter protein dynamics. It is a common feature in enzymes that control metabolic flux, signaling proteins, and receptors.

Prominent examples include hemoglobin, which shows cooperativity in oxygen binding; aspartate transcarbamoylase (ATCase) regulated by CTP and ATP; phosphofructokinase-1 (PFK-1) regulated by ATP, AMP and citrate; and many allosteric enzymes in glycolysis and biosynthesis. Allosteric sites provide targets for drugs and enzymes engineering.

Understanding allostery helps explain how proteins integrate cellular signals and adapt activities without requiring changes at the active site. It remains a central topic in biochemistry and pharmacology.