Structural changes accompanying enzymatic activation of human Hageman factor

Area of Science:

• Biochemistry
• Hematology
• Protein Chemistry

Background:

• Hageman factor (coagulation factor XII) is a key protein in the intrinsic pathway of blood coagulation.
• Understanding its structure and activation is crucial for comprehending hemostasis and thrombosis.
• Previous studies have indicated its role in activating other plasma proteases.

Purpose of the Study:

• To characterize the structure of purified Hageman factor from human plasma.
• To investigate the molecular changes occurring upon enzymatic activation.
• To identify the specific fragment responsible for prekallikrein activation.

Main Methods:

• Isolation and purification of Hageman factor from human plasma.
• Analysis of molecular weight and sedimentation properties (4.5S).
• Amino acid analysis.
• Enzymatic treatment with kallikrein, plasmin, and trypsin.
• Analysis of resulting fragments by molecular weight.
• Assessment of prekallikrein-activating ability of fragments.

Main Results:

• Purified Hageman factor is a single polypeptide chain with a molecular weight of 80,000.
• Enzymatic activation by kallikrein, plasmin, or trypsin cleaves Hageman factor into 52,000, 40,000, and 28,000 mol wt fragments.
• The 28,000 mol wt fragment was exclusively responsible for prekallikrein activation.

Conclusions:

• Hageman factor undergoes specific cleavage upon activation, generating distinct fragments.
• The 28,000 mol wt fragment plays a critical role in initiating the kallikrein-kinin system.
• This study elucidates the structural basis for Hageman factor's enzymatic activity.