Waldman S A, Rapoport R M, Fiscus R R, Leitman D C, Chang L Y, Murad F
Department of Medicine, Stanford University, Palo Alto, CA 94304.
Biochim Biophys Acta. 1989 Nov 30;999(2):157-62. doi: 10.1016/0167-4838(89)90212-4.
Structural analogs of atriopeptins (APs) were compared for their ability to activate particulate guanylate cyclase and bind to specific receptors in rat adrenal membranes. All analogs tested increase Vmax without altering the concentration of substrate required for half-maximum activity or the positive coperativity exhibited by the enzyme. Maximum velocities (pmoles of cGMP produced per min per mg protein) achieved in the absence and presence of APs were 128.3 +/- 6.6 and 283.8 +/- 20.6 using Mn2+-GTP, and 53.7 +/- 3.7 and 149.9 +/- 7.6 using Mg2+-GTP as the substrate, respectively. Although all APs were equally efficacious in activating the enzyme, their rank potency was ANF (8-33) = AP III = AP II greater than AP I when either divalent cation was used as the cofactor. The EC50 for activation of guanylate cyclase by AP I was about 10(-7) M, while that for the other peptides was about 10(-8) M, using either divalent cation cofactor. 125I-labeled ANF bound to rat adrenal membranes with a KD of 5.10(-10) M. Although all APs were equally efficacious in competing with labeled ANF for receptor binding, their rank potency was identical to that for enzyme activation. The Ki for AP I was about 10(-8) M, while that for the other peptides was about 10(-10) M. These data suggest that the carboxy terminal Phe-Arg present in the AP analogs except AP I and critical for biological and receptor-binding activity are also important in coupling receptor-ligand interaction with guanylate cyclase activation. The correlation between the rank order potency for receptor binding, enzyme activation, and the reported physiological actions of APs support the suggestion of a functional coupling between these proteins.
比较了心房肽（APs）的结构类似物激活大鼠肾上腺膜中颗粒型鸟苷酸环化酶和与特异性受体结合的能力。所有测试的类似物均增加了最大反应速度（Vmax），而不改变达到最大活性一半时所需的底物浓度或该酶所表现出的正协同性。在不存在和存在APs的情况下，分别以Mn2 + -GTP为底物时，产生的最大反应速度（每分钟每毫克蛋白质产生的cGMP皮摩尔数）为128.3±6.6和283.8±20.6；以Mg2 + -GTP为底物时，分别为53.7±3.7和149.9±7.6。尽管所有APs在激活该酶方面同样有效，但当使用任何一种二价阳离子作为辅助因子时，它们的效价顺序为心房钠尿肽（8 - 33）= AP III = AP II＞AP I。使用任何一种二价阳离子辅助因子时，AP I激活鸟苷酸环化酶的半数有效浓度（EC50）约为10^(-7) M，而其他肽的约为10^(-8) M。125I标记的心房钠尿肽与大鼠肾上腺膜结合，解离常数（KD）为5.1×10^(-10) M。尽管所有APs在与标记的心房钠尿肽竞争受体结合方面同样有效，但它们的效价顺序与酶激活的效价顺序相同。AP I的抑制常数（Ki）约为10^(-8) M，而其他肽的约为10^(-10) M。这些数据表明，除AP I外，AP类似物中存在的羧基末端苯丙氨酸 - 精氨酸对生物学和受体结合活性至关重要，在将受体 - 配体相互作用与鸟苷酸环化酶激活偶联方面也很重要。受体结合、酶激活的效价顺序以及所报道的APs的生理作用之间的相关性支持了这些蛋白质之间存在功能偶联的观点。
