Equally important is protein tyrosine phosphatase 1B (PTP1B), a pivotal intracellular non-transmembrane enzyme that exerts a suppressive effect on insulin signaling pathways: selective inhibition of the activity of PTP1B enhances cellular glucose uptake and counteracts the insulin resistance that typifies T2DM [7]. The gene discussed is PTPN1; the disease is type 2 diabetes mellitus.