Activation of normal and abnormal human factor IX with trypsin

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Factor IX activation is crucial for blood coagulation.
• Factor IX Chapel Hill (IXCH) mutation affects activation by factor XIa.
• Understanding alternative activation pathways is important for hemophilia B research.

Purpose of the Study:

• To investigate trypsin's ability to activate normal factor IX and IXCH.
• To characterize the activation products and their clotting activities.
• To examine the role of metal ions in factor IXa stability.

Main Methods:

• Enzymatic activation of factor IX and IXCH using trypsin and factor XIa.
• Amino-terminal amino acid sequencing to identify cleavage sites.
• Clotting assays to determine enzymatic activity.
• Metal ion protection assays against trypsin inactivation.

Main Results:

• Trypsin activates factor IX and IXCH to fully active IXa beta forms, similar to factor XIa activation.
• IXCH is cleaved by trypsin at Arg180-Val181 and Lys142-Leu143, releasing a larger activation peptide.
• Metal ions (Ca2+, Mn2+, Mg2+) protect factor IXa from trypsin-mediated inactivation, with Ca2+ and Mn2+ being most effective.

Conclusions:

• Trypsin is a potent activator of factor IX and IXCH, yielding fully active enzymes.
• Metal ions are critical for stabilizing factor IXa against proteolytic degradation.
• These findings offer insights into factor IX activation mechanisms and potential therapeutic strategies.