Boman B M, Zschunke M A, Scott R E
J Cell Physiol. 1984 Nov;121(2):357-67. doi: 10.1002/jcp.1041210213.
The plasma membrane of 3T3 cells contains at least two different endogenous cyclic AMP-dependent protein kinase systems. One catalyzes the phosphorylation of endogenous protein substrates, i.e., PP24 and PP14, whereas the other catalyzes the phosphorylation of exogenous substrates. In this paper the topography of these cyclic AMP-dependent phosphorylation systems is described. The results show that the kinases which phosphorylate only exogenous substrates are primarily localized to the outer plasma membrane surface whereas the endogenous cyclic AMP-dependent protein kinase and its two endogenous substrates are localized to the cytoplasmic plasma membrane surface. The data also establish that neither the cytoplasmically orientated kinase nor its substrates has a transmembrane orientation even though factors acting on the outer plasma membrane can affect these proteins. This suggests that functional modulation of the cytoplasmically localized cyclic AMP-dependent phosphorylation system can be mediated by a transmembrane regulatory mechanism. The importance of determining the topography of such plasma membrane phosphorylation systems is emphasized by recent studies which show that neoplastic transformation can be mediated at least in part by protein kinases and/or phosphoproteins which are localized on the cytoplasmic surface of the plasma membrane.
3T3细胞的质膜含有至少两种不同的内源性环磷酸腺苷依赖性蛋白激酶系统。一种催化内源性蛋白质底物（即PP24和PP14）的磷酸化，而另一种催化外源性底物的磷酸化。本文描述了这些环磷酸腺苷依赖性磷酸化系统的拓扑结构。结果表明，仅磷酸化外源性底物的激酶主要定位于质膜外表面，而内源性环磷酸腺苷依赖性蛋白激酶及其两种内源性底物定位于细胞质质膜表面。数据还证实，即使作用于质膜外表面的因子会影响这些蛋白质，位于细胞质中的激酶及其底物也没有跨膜取向。这表明细胞质中定位的环磷酸腺苷依赖性磷酸化系统的功能调节可由跨膜调节机制介导。最近的研究强调了确定这种质膜磷酸化系统拓扑结构的重要性，这些研究表明肿瘤转化至少部分可由位于质膜细胞质表面的蛋白激酶和/或磷蛋白介导。
