Adamo M L, Dyckes D F, Hazelwood R L
Endocrinology. 1983 Aug;113(2):508-16. doi: 10.1210/endo-113-2-508.
The interaction of pancreatic polypeptide (PP) with possible chicken and rat target tissues was investigated by characterizing the binding and degradation of [125I]iodo-PP by plasma membrane preparations in vitro. Membranes from chick brain and liver possessed highly specific avian PP (APP)-binding sites, while those from chick whole pancreas and proventricular and duodenal mucosa exhibited little or no specific [125I]iodo-APP binding. The affinity of the specific chick liver binding sites for APP was low; 500 ng unlabeled APP/ml (1.2 X 10(-7) M) were required for half-maximal displacement of [125I]iodo-APP. Chick brain membranes, on the other hand, possessed two orders of APP binding sites, a high affinity site (Kd = 3.3 X 10(-10) M) and a low affinity site (Kd = 1.8 X 10(-7) M). The binding process to chick brain membranes retained specificity for intact APP1-36, as unlabeled bovine PP1-36 (BPP1-36) inhibited specific binding of [125I]iodo-APP by 50% at a concentration of 7 X 10(-9) M (10 times the IC50 level of unlabeled APP). Carboxy-terminal pentapeptides of APP and BPP (APP32-36 and BPP32-36) interacted with the chick brain membrane APP-binding sites, but did not possess the full binding activity of the intact molecule. Membranes from rat brain exhibited little APP-specific binding and no BPP-specific binding. Chick kidney membranes degraded more [125I]iodo-APP than any other chicken tissue. The degradation process was specifically inhibited by unlabeled APP and yielded reaction products of lower molecular weight than intact APP. The antiprotease bacitracin was capable of virtually complete degradation inhibition, but its presence failed to increase APP binding by kidney membranes. It is concluded that chick brain possesses high affinity APP-binding sites, potentially functional at physiological concentrations of the polypeptide. APP-binding sites on liver membranes are probably physiologically nonfunctional, while the kidney is most active relative to other tissues in the degradation and, probably, clearance of APP.
通过体外对质膜制剂中[125I]碘代胰多肽（PP）的结合和降解进行表征，研究了胰多肽（PP）与可能的鸡和大鼠靶组织之间的相互作用。鸡脑和肝的膜具有高度特异性的禽胰多肽（APP）结合位点，而来自鸡全胰腺、前胃和十二指肠黏膜的膜则几乎没有或没有特异性的[125I]碘代APP结合。鸡肝特异性结合位点对APP的亲和力较低；半数最大位移[125I]碘代APP需要500 ng未标记的APP/ml（1.2×10−7 M）。另一方面，鸡脑膜具有两级APP结合位点，一个高亲和力位点（Kd = 3.3×10−10 M）和一个低亲和力位点（Kd = 1.8×10−7 M）。与鸡脑膜的结合过程对完整的APP1 - 36保持特异性，因为未标记的牛胰多肽1 - 36（BPP1 - 36）在浓度为7×10−9 M（未标记APP的IC50水平的10倍）时抑制[125I]碘代APP的特异性结合达50%。APP和BPP的羧基末端五肽（APP32 - 36和BPP32 - 36）与鸡脑膜APP结合位点相互作用，但不具有完整分子的全部结合活性。大鼠脑膜几乎没有APP特异性结合，也没有BPP特异性结合。鸡肾膜比任何其他鸡组织降解更多的[125I]碘代APP。降解过程被未标记的APP特异性抑制，产生的反应产物分子量低于完整的APP。抗蛋白酶杆菌肽几乎能够完全抑制降解，但其存在未能增加肾膜对APP的结合。结论是鸡脑具有高亲和力的APP结合位点，在该多肽的生理浓度下可能具有功能。肝细胞膜上的APP结合位点可能在生理上无功能，而相对于其他组织，肾在APP的降解以及可能的清除方面最为活跃。
