Lamensa J W, Moscarello M A
Department of Biochemistry, Hospital for Sick Children, Toronto, Ontario, Canada.
J Neurochem. 1993 Sep;61(3):987-96. doi: 10.1111/j.1471-4159.1993.tb03612.x.
A peptidylarginine deiminase (PAD; EC 3.5.3.15) has been isolated from bovine brain and some of its characteristics have been studied. The enzyme showed an absolute requirement for Ca2+, a temperature optimum at approximately 50 degrees C, and two Km values when benzoylarginine ethyl ester was used as substrate, 0.78 mM and 11.2 mM. The higher Km has not been reported previously. Protein substrates for the enzyme included polyarginine and myelin basic protein but not histones. Because one of the components of MBP contains six citrullinyl residues per mole, enzymic deimination appeared to be a likely mechanism. When the most cationic component (C-1) was subjected to PAD in solution, 17 of the 19 arginyl residues were modified. From sequence analyses we concluded that the nature of the amino acid residues adjacent to the deiminated arginine were not modifiers of the reaction as arginyl residues in a variety of environments were deiminated. This deimination was reflected in a large increase in random structure, as measured by [theta]200. At 5 degrees C, the [theta]200 of the deiminated protein was -70 x 10(3) compared with -30 x 10(3) deg.cm2/dmol for the native protein. When the temperature was increased to 70 degrees C, the [theta]200 was -44 x 10(3) for the deiminated protein and -20 x 10(7) deg.cm2/dmol for the native C-1. When plotted as a function of temperature, [theta]200 decreased linearly from 5 degrees C to 50 degrees C for both proteins and did not change from 50 degrees C to 70 degrees C. PAD provides a mechanism for deimination of arginyl residues of myelin basic protein. The selective deimination of the six arginyl residues that are consistently found deiminated in C-8 may be determined by the orientation of the protein in the membrane and/or the more complex lipid composition of myelin may affect the selectivity of the deimination.
一种肽基精氨酸脱亚氨酶（PAD；EC 3.5.3.15）已从牛脑中分离出来，并对其一些特性进行了研究。该酶对Ca2+有绝对需求，最适温度约为50℃，以苯甲酰精氨酸乙酯为底物时具有两个Km值，分别为0.78 mM和11.2 mM。较高的Km值此前未见报道。该酶的蛋白质底物包括聚精氨酸和髓鞘碱性蛋白，但不包括组蛋白。由于髓鞘碱性蛋白的一个组分每摩尔含有六个瓜氨酸残基，酶促脱亚胺作用似乎是一种可能的机制。当最具阳离子性的组分（C-1）在溶液中接受PAD作用时，19个精氨酸残基中有17个被修饰。通过序列分析我们得出结论，脱亚胺化精氨酸相邻氨基酸残基的性质不是反应的调节剂，因为处于各种环境中的精氨酸残基都会被脱亚胺化。这种脱亚胺化反映在无规结构的大幅增加上，通过[θ]200测量。在5℃时，脱亚胺化蛋白的[θ]200为-70×10³，而天然蛋白为-30×10³度·厘米²/摩尔。当温度升至70℃时，脱亚胺化蛋白的[θ]200为-44×10³，天然C-1为-20×10⁷度·厘米²/摩尔。当作为温度的函数绘制时，两种蛋白质的[θ]200从5℃到50℃呈线性下降，从50℃到70℃不变。PAD为髓鞘碱性蛋白精氨酸残基的脱亚胺化提供了一种机制。在C-8中始终发现被脱亚胺化的六个精氨酸残基的选择性脱亚胺化可能由蛋白质在膜中的取向决定，和/或髓鞘更复杂的脂质组成可能影响脱亚胺化的选择性。
