Inoue T, Hasumi K, Sugimoto M, Endo A
Department of Applied Biological Science, Tokyo Noko University, Fuchu, Japan.
Thromb Haemost. 1998 Mar;79(3):591-6.
Plactin D, a cyclic pentapeptide [cyclo(-D-Val-L-Leu-D-Leu-L-Phe-D-Arg-)] produced by a fungal strain, enhances fibrinolytic activity (6). The present study deals with the structure-activity relationship of plactins and their effects in U937 cells and mice. The results obtained from 50 plactin D analogues with a single amino acid substitution demonstrated that the following substitutions were detrimental: the enantiomer for each of the five residues; a polar, an acidic or a basic residue for D-Val, L-Leu, D-Leu or L-Phe; a polar, a hydrophobic or an acidic residue for D-Arg. On the other hand, a compound with L-Leu or L-Val in place of L-Phe was seven times as active as plactin D. These results suggest an essential role of a sterically restricted arrangement of four hydrophobic residues and the adjacent basic residue. The enhancement of fibrinolysis was dependent on plasma, ranging from 2- to 3-fold when U937 cells were incubated with 15-30 microM plactin D in the presence of 6-50% plasma, while no elevation was observed when cells were incubated in the absence of plasma. Plasminogen alone could not substitute for plasma. The plactin D effect was totally abolished by anti-urokinase IgG but not by anti-tissue plasminogen activator IgG. Plactin D caused a plasma-dependent, transient increase in the cellular urokinase activity. This urokinase activation may have accounted for the increased fibrinolytic activity of plactin D-treated U937 cells. Homogenates of the lung obtained from mice 0.5 to 2 h after intravenous plactin D (5 mg/kg) showed 2- to 3-fold increased levels of fibrinolytic activity, while activities of the brain, heart, liver, spleen, kidney and aorta were not significantly affected. In conclusion, plactin D enhances fibrinolysis both in cultured mammalian cells and in experimental animals.
普拉汀D是一种由真菌菌株产生的环五肽[环（-D-缬氨酸-L-亮氨酸-D-亮氨酸-L-苯丙氨酸-D-精氨酸-）]，可增强纤溶活性（6）。本研究探讨了普拉汀类化合物的构效关系及其对U937细胞和小鼠的影响。从50种具有单个氨基酸取代的普拉汀D类似物获得的结果表明，以下取代是有害的：五个残基中每个残基的对映体；D-缬氨酸、L-亮氨酸、D-亮氨酸或L-苯丙氨酸的极性、酸性或碱性残基；D-精氨酸的极性、疏水或酸性残基。另一方面，用L-亮氨酸或L-缬氨酸取代L-苯丙氨酸的化合物活性是普拉汀D的七倍。这些结果表明四个疏水残基和相邻碱性残基的空间受限排列起着至关重要的作用。纤溶增强依赖于血浆，当U937细胞在6 - 50%血浆存在下与15 - 30 microM普拉汀D孵育时，纤溶增强2至3倍，而在无血浆条件下孵育细胞时未观察到升高。单独的纤溶酶原不能替代血浆。普拉汀D的作用被抗尿激酶IgG完全消除，但不被抗组织纤溶酶原激活物IgG消除。普拉汀D导致细胞尿激酶活性出现血浆依赖性的短暂增加。这种尿激酶激活可能解释了经普拉汀D处理的U937细胞纤溶活性的增加。静脉注射普拉汀D（5 mg/kg）后0.5至2小时从小鼠获得的肺匀浆显示纤溶活性水平增加2至3倍，而脑、心脏、肝脏、脾脏、肾脏和主动脉的活性未受到显著影响。总之，普拉汀D在培养的哺乳动物细胞和实验动物中均增强纤溶作用。
