Alpha-4 beta-2 nicotinic receptor
The alpha-4 beta-2 nicotinic receptor, also known as the α4β2 receptor, is a type of nicotinic acetylcholine receptor implicated in learning, consisting of α4 and β2 subunits. It is located in the brain, where activation yields post- and presynaptic excitation, mainly by increased Na and K permeability. Stimulation of this receptor subtype is also associated with growth hormone secretion. People with the inactive CHRNA4 mutation Ser248Phe are an average of 10 cm (4 inches) shorter than average and predisposed to obesity. A 2015 review noted that stimulation of the α4β2 nicotinic receptor in the brain is  responsible for certain improvements in attentional performance; among the nicotinic receptor subtypes, nicotine has the highest binding affinity at the α4β2 receptor (k=1 ), which is also the primary biological target that mediates nicotine's addictive properties. The receptors exist in the two stoichiometries: Structure. The x-ray structure of the (α4)(β2) receptor is known since 2016 and reveals a circular α–β–β–α–β ordering of subunits.