KINETIC PROPERTIES OF ARGININE KINASE ISOENZYMES OF LIMULUS POLYPHEMUS
KINETIC PROPERTIES OF ARGININE KINASE ISOENZYMES OF LIMULUS POLYPHEMUS
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DOI：
10.1016/0003-9861(72)90319-0
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发表时间：
1972-01-01
影响因子：
3.9
通讯作者：
BLETHEN, SL
中科院分区：
文献类型：
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作者：
BLETHEN, SL
本文研究了从河蟹体内分离的负性和中性精氨酸激酶的一些动力学性质。两种形式的精氨酸激酶表现出非常相似的动力学性质。两者都需要二价阳离子，如镁离子或锰离子才能起作用。Ca~(2+)的活性约为Mg~(2+)的40%，而锌、铜、铁和铁不是活化剂。高浓度的游离镁离子对这两种酶均有抑制作用。在正向反应中，当游离镁离子浓度为1 mM时，酶活性最高，其他核苷三磷酸可以替代ATP作为正向反应的底物。对于这两种形式，V的递减顺序是ATP2‘dATPITP；⋙；GTP。L-精氨酸是两种同工酶的底物，但它们都是竞争性的抑制剂。l-刀豆氨酸是两种形式的底物，但其最适速度远低于l-精氨酸的底物。L-刀豆氨酸对两种形式的反应都表现为S型动力学。正向反应的初始速度研究结果表明，这两种形式的机理都是随机顺序快速平衡型，类似于兔肌肉肌酸激酶和长尾白兔精氨酸激酶的机理。用负性形式进行的同位素交换测量也符合这一机制。尽管没有发现两种形式之间功能差异的催化基础，但在体外稳定性的差异可能反映了活体的稳定性，从而为调节各种组织中的精氨酸激酶水平提供了基础，从而为具有这两种形式的物种提供了选择优势。
A number of kinetic properties of the negative and neutral arginine kinases isolated from the horseshoe crab,Limulus polyphemus, were studied. The two arginine kinase forms show very similar kinetic properties. Both require a divalent cation such as Mg2+or Mn2+for activity. Ca2+is about 40% as active as Mg2+while Zn2+, Cu2+, Fe2+and Fe3+are not activators. High concentrations of free Mg2+will inhibit both enzymes. Optimal enzyme activity is observed in the forward reaction when the concentration of free Mg+is 1 mm.Other nucleoside triphosphates can substitute for ATP as substrates in the forward reaction. The order of decreasingVis ATP > 2′dATP ⋙ ITP > GTP for both forms. Neitherd-arginine norl-argininic acid will act as substrates for either isoenzyme, but both compounds are competitive inhibitors with respect, tol-arginine.l-Canavanine is a substrate for both forms, but its optimal velocity is much less than that observed withl-arginine.l-Canavanine shows sigmoid kinetics with both forms.The results of initial velocity studies of the forward reaction indicate that the mechanism for both forms is of the random order rapid equilibrium type similar to that observed with rabbit muscle creatine kinase andPanulirus longipesarginine kinase. Isotope-exchange measurements made with the negative form were also consistent with this mechanism.Although no catalytic basis for a functional difference between the two forms was found, it is possible thatin vitrodifferences in stability may reflect stabilitiesin vivoand thus provide a basis for regulating arginine kinase levels in various tissues thereby giving a selective advantage to species having both forms.