Grant: Operating Grant

The circulatory system can elicit a complex mechanism known as the blood coagulation cascade to make the blood clot. The mechanism is for the most part latent, but it is locally activated when needed to prevent excessive blood loss in the event of injury. Once activated, the cascade can be very powerful; if it is not properly regulated it can have rapid and lethal consequences, such as heart attack and stroke. The prothrombinase complex operates within the cascade and catalyses the formation of the blood clotting enzyme thrombin from its latent precursor, prothrombin. The proposed work is directed at obtaining a better understanding of the functional properties of this complex. The work will be accomplished by measuring the function of the complex reconstructed from purified components. Its down regulation by two physiologic regulators, known as antithrombin and activated protein C, will be quantitatively characterized in real time during the process of prothrombin activation. The mechanism of prothrombin activation will be investigated in molecular detail. The binding of prothrombin and thrombin to blood platelets and the consequences of that binding will be measured. In addition, a determination of whether prothombinase exhibits thresholding, all-or-none qualities will be made. If so, a fundamentally new view of the regulation of prothrombinase will arise. These studies should provide a clearer picture of how prothrombinase works and is regulated. This clearer understanding will provide both new insights into the molecular details which underlie dysfunctional operation of the cascade and new rationale for reducing or preventing heart attacks and strokes with drugs.