= Insulin receptor
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The mature <insulin receptor> already contains two extracellular $\alpha$ chains and two membrane-spanning $\beta$ chains, joined through <protein disulfide bonds>, before <insulin> binds. <Insulin> induces rearrangement of this $(\alpha\beta)_2$ assembly. Partner-mediated <phosphorylation> of the inhibitory activation loop permits increased <protein kinase> activity. Ligand-induced creation of a previously absent dimer is therefore an unsuitable universal explanation.<Cell signaling by receptor-tyrosine kinases by Mark A Lemmon and Joseph Schlessinger>[“Mechanisms of Receptor Activation” and “TKD autoinhibition by the activation loop: insulin and FGF receptors”, Figure 2E]{ref}
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