West D W, Clegg R A
Eur J Biochem. 1983 Dec 1;137(1-2):215-20. doi: 10.1111/j.1432-1033.1983.tb07817.x.
A Golgi vesicle preparation isolated from the mammary tissue of rats in mid-lactation has been shown to contain the caseins of rat milk. These proteins were phosphorylated when the Golgi vesicles were incubated in the presence of [gamma-32P]ATP. Although this phosphorylation occurred when the physical integrity of the vesicles was maintained, it was markedly increased when the membrane structure was disrupted by hypoosmotic conditions or by use of detergents. The kinase responsible has been shown to be responsive to the intravesicular concentration of Ca2+ and to the extravesicular concentration of Mg2+. These results have been interpreted in terms of a model suggesting a transmembrane location for the enzyme with binding sites on the cytosolic membrane face for Mg2+ and possibly also for ATP and on the luminal surface for Ca2+ and the caseins. Others have postulated that the assembly of caseins into micelles occurs in Golgi vesicles and requires both prior phosphorylation of the proteins and the presence of Ca2+. In this investigation we demonstrate that treatments which increase the intravesicular casein phosphorylation also alter the Ca2+ balance within the vesicle lumen. These results are discussed in relation to the ATP-dependent accumulation of Ca2+ by the mammary gland Golgi vesicles.
从处于泌乳中期的大鼠乳腺组织中分离出的高尔基体囊泡制剂已被证明含有大鼠乳汁中的酪蛋白。当高尔基体囊泡在[γ-32P]ATP存在的情况下孵育时，这些蛋白质会发生磷酸化。尽管这种磷酸化在囊泡的物理完整性得以维持时就会发生，但当膜结构因低渗条件或使用去污剂而被破坏时，磷酸化会显著增加。已证明负责的激酶对囊泡内Ca2+浓度和囊泡外Mg2+浓度有反应。这些结果已根据一个模型进行了解释，该模型表明该酶位于跨膜位置，在细胞质膜表面有Mg2+以及可能还有ATP的结合位点，在腔表面有Ca2+和酪蛋白的结合位点。其他人推测酪蛋白组装成胶束发生在高尔基体囊泡中，并且需要蛋白质预先磷酸化以及Ca2+的存在。在本研究中，我们证明增加囊泡内酪蛋白磷酸化的处理也会改变囊泡腔内的Ca2+平衡。这些结果将结合乳腺高尔基体囊泡对Ca2+的ATP依赖性积累进行讨论。
