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Interaction of pregnancy-associated plasma protein-A (PAPP-A) with coagulation: a bioassay for PAPP-A
Insights
Pregnancy-associated plasma protein A (PAPP-A) inhibits blood clotting by potentiating antithrombin III, similar to heparin. This interaction enabled the development of a sensitive bioassay for PAPP-A activity.
Area of Science:
- Biochemistry
- Hematology
- Reproductive Biology
Background:
- Pregnancy-associated plasma protein A (PAPP-A) levels differ between plasma and serum.
- PAPP-A exhibits heparin-binding properties, suggesting interactions with the coagulation system.
Purpose of the Study:
- To investigate the interaction between PAPP-A and the blood clotting cascade.
- To develop a bioassay for measuring PAPP-A activity based on its anticoagulant properties.
Main Methods:
- Assessing the effect of purified PAPP-A on thrombin-induced coagulation of citrated plasma.
- Evaluating the necessity of antithrombin III (AT III) for PAPP-A's inhibitory effect.
- Developing a bioassay measuring thrombin-induced fibrinogen polymerization spectrophotometrically.
- Comparing the inhibitory kinetics of PAPP-A and heparin.
Main Results:
- Pure PAPP-A inhibits thrombin-induced coagulation, requiring the presence of AT III.
- PAPP-A's anticoagulant effect is analogous to heparin's.
- A linear relationship was observed between residual thrombin activity and PAPP-A concentration.
- The developed bioassay demonstrated high sensitivity and reproducibility with first-order kinetics for inhibition.
Conclusions:
- PAPP-A possesses anticoagulant properties mediated through AT III.
- A novel bioassay utilizing PAPP-A's interaction with the clotting system was successfully developed.
- The bioassay allows for the comparison of PAPP-A activities from various sources.
Abstract:
The observation that pregnancy-associated plasma protein A (PAPP-A) concentrations are higher in plasma compared to serum obtained from the same patient, together with fact that PAPP-A binds to heparin, prompted us to study the interaction between PAPP-A and the clotting system. It was determined that pure PAPP-A inhibits thrombin-induced coagulation of citrated plasma. The presence of antithrombin III (AT III) was necessary since PAPP-A had no inhibitory effect on coagulation of AT III-depleted plasma. The effect of PAPP-A is thus similar to that of heparin. This property of PAPP-A was used to develop a bioassay. Thrombin-induced polymerization of purified fibrinogen was measured in a spectrophotometer. AT III is a weak inhibitor of polymerization, but its effect is magnified in the presence of PAPP-A or heparin. The residual thrombin activity, when plotted against the concentration of PAPP-A, gives a linear relationship. The assay conditions developed allow maximal sensitivity and reproducibility. The kinetics of inhibition due to PAPP-A and heparin was first order. With this bioassay, activities of PAPP-A molecules isolated by the same technique from different fetomaternal compartments were compared.