Jiang Y P, Muller-Esterl W, Schmaier A H
Thrombosis Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
J Biol Chem. 1992 Feb 25;267(6):3712-7.
High and low molecular weight kininogens (HK and LK) are able to bind to platelets to inhibit thrombin binding to and activation of platelets. The heavy chain domain on the kininogens that contains these functions has been determined. Domain 3 (D3) but not domains 1 or 2, completely inhibited 125I-HK binding to platelets (Ki = 24 +/- 7 nM, n = 4). 125I-D3 specifically bound to unstimulated platelets and human umbilical vein endothelial cells. On platelets, it was blocked by unlabeled D3 and HK but not prekallikrein, factor XII, C1s, or C1 inhibitor. Further, one monoclonal antibody (HKH13) directed to kininogens' D3 blocked 125I-HK and 125I-D3 binding to platelets. The binding of 125I-D3 to platelets was fully reversible by addition of 35 molar excess of unlabeled D3. D3 binding to platelets was saturable with an apparent Kd of 39 +/- 8 nM (n = 4) and 1227 +/- 404 binding sites/platelet. D3, like HK and LK, inhibited thrombin-induced platelet activation by preventing thrombin binding to platelets. Another monoclonal antibody (HKH12), directed to D3, which did not block HK binding to platelets, reduced HK's ability to inhibit 125I-alpha-thrombin binding. This result suggests that the region on D3 that inhibits 125I-alpha-thrombin binding to platelets is different from that which directly binds to platelets. These studies indicate that D3 of the kininogens contains both a binding region for platelets and endothelial cells and another region that inhibits thrombin-induced platelet activation.
高分子量和低分子量激肽原（HK和LK）能够与血小板结合，以抑制凝血酶与血小板的结合及血小板的激活。已确定激肽原上包含这些功能的重链结构域。结构域3（D3）而非结构域1或2能完全抑制¹²⁵I-HK与血小板的结合（Ki = 24 ± 7 nM，n = 4）。¹²⁵I-D3特异性结合未受刺激的血小板和人脐静脉内皮细胞。在血小板上，它被未标记的D3和HK阻断，但不受前激肽释放酶、因子Ⅻ、C1s或C1抑制剂的阻断。此外，一种针对激肽原D3的单克隆抗体（HKH13）可阻断¹²⁵I-HK和¹²⁵I-D3与血小板的结合。加入35倍摩尔过量的未标记D3可使¹²⁵I-D3与血小板的结合完全逆转。D3与血小板的结合具有饱和性，表观解离常数Kd为39 ± 8 nM（n = 4），每个血小板有1227 ± 404个结合位点。与HK和LK一样，D3通过阻止凝血酶与血小板结合来抑制凝血酶诱导的血小板激活。另一种针对D3的单克隆抗体（HKH12）虽不阻断HK与血小板的结合，但降低了HK抑制¹²⁵I-α-凝血酶结合的能力。这一结果表明，D3上抑制¹²⁵I-α-凝血酶与血小板结合的区域与直接结合血小板的区域不同。这些研究表明，激肽原的D3既包含与血小板和内皮细胞的结合区域，又包含另一个抑制凝血酶诱导的血小板激活的区域。
