Purushotham K R, Paul G A, Wang P, Humphreys-Beher M G
Department of Oral Biology, University of Florida, Gainesville 32610.
Life Sci. 1994;54(16):1185-94. doi: 10.1016/0024-3205(94)00840-x.
Rat parotid glands were shown to possess protein phosphatase activity capable of catalyzing the dephosphorylation of several model phosphatase substrates, including p-nitrophenyl phosphate, tyrosine phosphorylated myelin basic protein and serine phosphorylated casein. A portion of this activity closely resembled dephosphorylation patterns of known protein tyrosine phosphatases. The reaction showed sensitivity to sodium orthovanadate, proceeded efficiently in the presence of metal chelators and favored acidic pH for optimum activity. Cell lysates from EGF- or isoproterenol-stimulated parotid glands, when immuno-precipitated with anti-Syp antibody, showed the induction of protein tyrosine phosphatase activity significantly higher than the unstimulated controls. The protein of M(r) = 65kDa also had elevated levels of tyrosine phosphorylation following isolation from cells treated to undergo proliferation. Thus parotid gland acinar cells possess protein tyrosine phosphatase activity of the PTPase 1D class associated with inducible cell growth, in addition to other phosphatases.
已证明大鼠腮腺具有蛋白质磷酸酶活性，能够催化几种模型磷酸酶底物的去磷酸化反应，这些底物包括对硝基苯磷酸酯、酪氨酸磷酸化的髓鞘碱性蛋白和丝氨酸磷酸化的酪蛋白。该活性的一部分与已知蛋白质酪氨酸磷酸酶的去磷酸化模式非常相似。该反应对原钒酸钠敏感，在金属螯合剂存在的情况下能高效进行，且在酸性pH条件下活性最佳。用抗Syp抗体进行免疫沉淀时，来自表皮生长因子（EGF）或异丙肾上腺素刺激的腮腺细胞裂解物显示，其蛋白质酪氨酸磷酸酶活性的诱导水平显著高于未刺激的对照。从经增殖处理的细胞中分离出的分子量为65kDa的蛋白质，其酪氨酸磷酸化水平也有所升高。因此，除了其他磷酸酶外，腮腺腺泡细胞还具有与诱导性细胞生长相关的PTPase 1D类蛋白质酪氨酸磷酸酶活性。
