JAK/STAT pathway activation by Ob-Rb leptin receptor mechanism. After leptin binding, the Ob-Rb receptor changes its conformation that leads to JAK translocation. JAK proteins become activated and start to exert their kinase activity and phosphorylate tyrosine residues of other JAK proteins and of Ob-Rb receptor. Tyr1138 phosphorylation allows STAT3 protein binding and next, STAT proteins become the substrate for JAK proteins related to Ob-R receptor. STAT3 protein phosphorylation leads to dissociation of the protein from the receptor, dimerization and translocation to the nucleus. After the translocation STAT proteins stimulate specific genes expression [according to [17, 24]].