Kahn D W, Besterman J M
Department of Cell Biology, Glaxo Inc., Research Triangle Park, NC 27709.
Proc Natl Acad Sci U S A. 1991 Jul 15;88(14):6137-41. doi: 10.1073/pnas.88.14.6137.
The phosphorylation of diacylglycerol (DG), a reaction catalyzed by DG kinase, may be critical in the termination of effector-induced signals mediated by protein kinase C. Synapsin I is a principal target of intracellular protein kinases and is thought to be involved in the release of neurotransmitter from axon terminals. We present several lines of evidence which indicate that rat brain synapsin, in addition to this role, may function as a DG kinase. Purified rat brain DG kinase was digested with trypsin, which produced three major fragments whose sequence was identical to three regions in synapsin I. Using a rabbit anti-synapsin polyclonal antiserum, the elution profile of synapsin immunoreactivity coincided exactly with that of DG kinase activity in column fractions from the final step in the DG kinase purification procedure. As is the case with synapsin, the purified enzyme was a strongly basic protein with an isoelectric point greater than 10.0. Finally, incubating the DG kinase with highly purified bacterial collagenase, an enzyme that partially degrades the proline- and glycine-rich synapsin, resulted in the simultaneous loss of DG kinase activity and synapsin immunoreactivity. We conclude that cytosolic rat brain synapsin is capable of functioning as a DG kinase.
二酰基甘油（DG）的磷酸化反应由DG激酶催化，这一反应可能在由蛋白激酶C介导的效应器诱导信号的终止过程中起关键作用。突触素I是细胞内蛋白激酶的主要作用靶点，被认为参与轴突末端神经递质的释放。我们提供了几条证据表明，大鼠脑突触素除了具有这一作用外，还可能作为一种DG激酶发挥功能。用胰蛋白酶消化纯化的大鼠脑DG激酶，产生了三个主要片段，其序列与突触素I中的三个区域相同。使用兔抗突触素多克隆抗血清，在DG激酶纯化过程最后一步的柱层析组分中，突触素免疫反应性的洗脱曲线与DG激酶活性的洗脱曲线完全一致。与突触素的情况一样，纯化的酶是一种强碱性蛋白，其等电点大于10.0。最后，用高度纯化的细菌胶原酶（一种能部分降解富含脯氨酸和甘氨酸的突触素的酶）孵育DG激酶，导致DG激酶活性和突触素免疫反应性同时丧失。我们得出结论，大鼠脑胞质中的突触素能够作为一种DG激酶发挥作用。
