Distinct subunits for the regulation and catalytic activity of aspartate transcarbamylase.
Distinct subunits for the regulation and catalytic activity of aspartate transcarbamylase.
复制标题
天冬氨酸转氨甲酰酶的调节和催化活性的不同亚基。
作者：
J. Gerhart;H. K. Schachman
摘要：该通信提出了直接的理化研究有关酶天冬氨酸转氨甲酰酶（ATCase）在其亚基结构和结合的特定抑制性代谢产物，胞苷三磷酸（CTP）。从沉降和粘度研究判断，来自大肠杆菌的ATCase是一种致密的球状蛋白，沉降系数（S20，w）为11.7 S，特性粘度为0.045 dl/g，分子量为310，000。CTP类似物，5-溴胞苷三磷酸（BrCTP）的结合的ultracenthegal分析，揭示了8个受体位点上的酶的存在。加入汞，对苯甲酸汞后，天然ATCase解离成两种类型的亚基，它们很容易通过柱层析的区域离心分离。较小的蛋白质称为调节亚基，具有抑制剂BrCTP的受体位点，并且是控制酶活性所必需的。由于调节亚基占天然酶总重量的37%，因此可以计算出每个ATCase分子中有四个这样的亚基。同样，可以得出结论，在天然酶含有两个催化亚基。
Abstract : The communication presents direct physiochemical studies concerning the enzyme aspartate transcarbamylase (ATCase) in terms of its subunit structure and binding of the specific inhibitory metabolite, cytidine triphosphate (CTP). As judged from sedimentation and viscosity studies, ATCase from Escherichia coli is a compact, globular protein with a sedimentation coefficient (S20,w) of 11.7 S, an intrinsic viscosity of 0.045 dl/g, and a molecular weight of 310,000. Ultracentrifugal analysis of the binding of the CTP analog, 5-bromocytidine triphosphate (BrCTP), reveals the existence of eight receptor sites on the enzyme. Upon the addition of the mercurial, p-mercuribenzoate, native ATCase dissociates into two types of subunits which are easily separable by zone centrifugation of column chromatography. The smaller protein, termed the regulatory subunit, bears the receptor sites for the inhibitor, BrCTP, and is required for the control of enzymic activity. Since the regulatory subunits comprise 37% of the total weight of the native enzyme, it can be calculated that there are four such subunits in each ATCase molecule. Similarly it can be concluded that in the native enzyme contains two catalytic subunits.