人凝血酶和浙江蝮蛇毒类凝血酶凝聚纤维蛋白原及释放血纤肽的不同机制

人纤维蛋白原经人凝血酶和浙江蝮蛇毒类凝血酶作用后,释放出血纤纤肽A和血纤肽B,二者可用高效液相色谱法分离鉴定。人凝血酶首先释放出血纤肽A,浙江蝮蛇毒类凝血酶则先释放出血纤肽B,甚至在纤维蛋白凝聚之前,血纤肽B的释放量早已达到极值,即使凝块形成后,血纤肽A与血纤肽B之比仍为1:3。人凝血酶在钙离子存在下,作用于纤维蛋白原时,其凝聚时间缩短,血纤肽A释放量不变,血纤肽B释放量则增高。在同样条件下,浙江蝮蛇毒类凝血酶作用时,血纤肽A释放量无明显变化,血纤肽B释放量却降低近1/3。无论是人凝血酶还是浙江蝮蛇毒类凝血酶,当与纤维蛋白原在2M尿素存在下反应时,均无可见凝块形成,但在37℃下用350nm光吸收监测其聚合过程仍可见光吸收上升,溶液呈乳白色。本文首次报道用电子显微镜观察比较了人凝血酶和浙江蝮蛇毒类凝血酶作用人纤维蛋白原后所形成的凝块结构。前者形成的结构致密,纤维长而细;后者形成的结构松散,较透明,纤维短而粗,这种结构更易为体内纤溶系统所降解。

DIFFERENT MECHANISMS OF FIBRIN POLYMERIZATlON AND FIBRINOPEPTIDE A AND B RELEASE INDUCED BY HUMAN THROMBIN AND THROMBIN-LIKE ENZYME FROM THE SNAKE VENOM OF AGKISTRODON HALYS PALLAS

Human fibrinopeptide A and B release either by human thrombin or by thrombin-like enzyme from the venom of Agkistrodon halys Pallas were quantitatively estimated by HPLC. In contrast to human thrombin, the thrombin-like enzyme predominantly released fibrinopeptide B which rapidly reached the maximum even before the aggregation of fibrin when monitored at 350 nm.The ratio of FPA/FPB (1:3) remained unchanged after a visible clot was observed. The effects of calcium ions on the release of fibrinopeptide A and B were investigated. The release of fibrinopeptide B was apparently enhanced with human thrombin and suppressed with the thrombin-like enzyme. On the contrary, there was no noticeable change in fibropeptide A release.In the presence of 2 M urea no visible clot could be found though the absorbance at 350 nm was stili observed to increase. The structure of fibrin caused by human thrombin or the thrombin-like enzyme was studied by elec tron microscopy. The fibrin clot formed by human thrombin was more compact, dense and stretched, with a fibre diameter of 60 to 150 nm, whereas the network of fibres formed by the thrombin-like enzyme was less compact, more transparent, with shorter fibres of diameter 150 to 250 nm. It indicated that in the latter case much more lateral aggregation had occurred because of the preferential release of fibrinopeptide B.