Enzymatic plasminogen activators

During platelet plug formation, the fibrinolytic pathway is locally activated. Plasminogen is enzymatically processed to plasmin (fibri-nolysin) by plasminogen activators present in the tissue. Plasmin interferes in clot propagation and dissolves the fibrin network as wounds heal. At present, a number of fibrinolytic enzymes are available for treatment of myocardial infarctions or pulmonary emboli (see p. 201). 

Parekh, R.B., Dwek, R.A., Rudd, P.M., Thomas, J.R., Rademacher, T.W., Warren, T., Wun, T.-C., Hebert, B., Reitz, B., Palmier, M., Ramabhadran, T., and Tiemeier, D.C. (1989). N-Glycosylation and in vitro enzymatic activity of human recombinant tissue plasminogen activator expressed in Chinese hamster ovary cells and a murine cell line. Biochemistry 28,7670 7679. 

Another approach for studying a cell s capacity to degrade a specific substrate lies midway between zymography and the immobilized component method described above. Here, the cells are seeded on the bottom of a dish, which is then overlaid with soft agar containing a substrate for proteolytic activity. After incubation under appropriate conditions, lithic plaques appear within the agar, indicative of enzymatic activity. The assay is described below to evidence urokinase-plasminogen activator (uPA) activity. 

A. Apffel, J.A. Chakel, W.S. Hancock, C. Souders, T. MTimkulu, E. Pungor, Jr., Application of LC-ESI-MS and MALDI-TOF-MS in combination with selective enzymatic modifications in the characterization of glycosylation patterns in singlechain plasminogen activator, J. Chromatogr. A, 732 (1996) 27. 

The authors suggested that the tissue-destructive activity of the trophoblast is probably plasmin-mediated, though the source of the plasminogen remains unclear relative to PA alone, the plasmin produced by plasminogen activation would provide a tremendous amplification of both the enzymatic activity and the substrate range, in keeping with the extensive tissue destruction observed during implantation. 

Ranby, M., N. Bergsdorf T. Nilsson, Enzymatic properties of the one- and two-chain form of tissue plasminogen activator. Thromh Res 1982, 27, 175-183. 

Zwickl CM, Hughes BL, Piroozi KS, Smith HW, Wierda D. Immunogenicity of tissue plasminogen activators in rhesus monkeys antibody formation and effects on blood level and enzymatic activity. Fundam Appl Toxicol 1996 30 243-254. 

Binbrek A, Rao N, Absher PM, Van de Werf E, Sobel BE. The relative rapidity of recanalization induced by recombinant tissue-type plasminogen activator (rt-PA) and TNK-tPA assessed with enzymatic methods. Coron Artery Dis 2000 11 429 35. 

Rdnby, N. Bergsdorf, and T. Nllson, Enzymatic Properties of One-and Two-Chain Forms of Tissue Plasminogen Activator, Throm. Res., 27 175-183 (1982). 

The coagulation system that generates thrombin consists of intrinsic and extrinsic pathways. Both pathways are composed of a series of enzymatic reactions eventually producing thrombin, fibrin, and a stable clot. In parallel with the coagulation, the fibrinolytic system is activated locally. Plasminogen is converted to plasmin, which dissolves the fibrin mesh1 2 3 (Fig. 64—1). 

Urokinase is a serine protease produced by the kidney and is found in both the plasma and urine. It is capable of proteolytically converting plasminogen into plasmin. Two variants of the enzyme have been isolated a 54 kDa species and a lower molecular mass (33 kDa) variant. The lower molecular mass form appears to be derived from the higher molecular mass moiety by proteolytic processing. Both forms exhibit enzymatic activity against plasminogen. 

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