Claim: PTPN1 isolated from a human placental protein extract (endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell), and is also in the cytoplasmic face; it can also be found in mice.
Evidence: PTP1B was first isolated from a human placental protein extract, but it is expressed in many tissues. PTP1B is localized to the cytoplasmic face of the endoplasmic reticulum. The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. In mice, genetic ablation of PTPN1 results in enhanced insulin sensitivity.