PTEN dephosphorylates PIP3

At the plasma membrane, phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase and dual-specificity protein phosphatase aka phosphatase and tensin homolog (PTEN) dephosphorylates phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) (Maehama & Dixon 1998, Myers et al. 1998, Das et al. 2003). The PI3K network is negatively regulated by phospholipid phosphatases that dephosphorylate PIP3, thus hampering AKT activation (Myers et al. 1998). The tumour suppressor PTEN is the primary phospholipid phosphatase.<br>Early studies indicated that magnesium ion, Mg2+, was needed for the catalytic activity of PTEN isolated from bovine thymus (Kabuyama et al. 1996). Subsequent studies have shown that PTEN was catalytically active in buffers free of magnesium and magnesium was not detected as part of the PTEN crystal (Lee et al. 1999).

在质膜上，磷脂酰肌醇-3,4,5-三磷酸磷酸酶及双特异性蛋白磷酸酶（又称磷酸酶和张力蛋白同源物，PTEN）通过去磷酸化磷脂酰肌醇-3,4,5-三磷酸（PI(3,4,5)P3）为磷脂酰肌醇-4,5-二磷酸（PI(4,5)P2）而发挥作用（Maehama & Dixon 1998，Myers et al. 1998，Das et al. 2003）。PI3K网络受磷脂磷酸酶的负向调控，这些磷酸酶通过去磷酸化PIP3来阻碍AKT的激活（Myers et al. 1998）。肿瘤抑制因子PTEN是主要的磷脂磷酸酶。<br>早期研究表明，牛胸腺中分离得到的PTEN的催化活性需要镁离子，Mg2+（Kabuyama et al. 1996）。后续研究则表明，PTEN在无镁离子的缓冲液中亦表现出催化活性，并且镁离子并未在PTEN的晶体结构中检测到（Lee et al. 1999）。