Partial purification and characterization of contact activation cofactor

Area of Science:

• Hematology
• Biochemistry
• Coagulation Cascade

Background:

• The intrinsic pathway of blood coagulation involves multiple factors, including Factor XI, Factor XII, and Fletcher factor.
• A previously unidentified activity, termed contact activation cofactor (CAC), is also implicated in this phase.
• These activities are diminished in plasma treated to remove specific components (Dicalite-adsorbed plasma).

Purpose of the Study:

• To define and characterize a novel cofactor in the intrinsic clotting pathway, designated contact activation cofactor (CAC).
• To develop an assay for quantifying CAC activity.
• To investigate the biochemical properties and potential identity of CAC with known clotting factors.

Main Methods:

• A modified activated partial thromboplastin time assay was developed using Dicalite-adsorbed plasma and purified clotting factors.
• Physicochemical properties of CAC were determined, including stability, pH optimum, and behavior during protein fractionation techniques (ammonium sulfate precipitation, A1(OH)3 adsorption, DEAE-cellulose chromatography, gel filtration).
• Purification of CAC was performed, and its activity was assessed in promoting the generation of activated Factor XI (XIa).

Main Results:

• A functional assay for CAC was established.
• CAC demonstrated stability at 56°C for 60 minutes, with gradual loss at 80°C, and was stable between pH 6-9.
• Purification yielded isolated CAC with an estimated molecular weight of 220,000 daltons, which promoted Factor XI activation and exhibited properties consistent with Fitzgerald factor.

Conclusions:

• Contact activation cofactor (CAC) is a distinct entity involved in the contact phase of intrinsic blood clotting.
• The characterized properties of CAC strongly suggest it is identical to Fitzgerald factor.
• Isolated CAC directly facilitates the activation of Factor XI, underscoring its role in the coagulation cascade.