Necessity of the divalent cation in the reaction between EAC1-8hu and C9gp

Area of Science:

• Biochemistry
• Immunology
• Complement System

Background:

• The formation of the terminal complement complex (TCC) is essential for the immune response.
• The specific conditions influencing the formation of the E* complex from EAC1-8hu and C9gp are not fully understood.
• EDTA is known to chelate divalent cations, which are often critical for enzymatic and binding activities.

Purpose of the Study:

• To investigate the role of divalent cations and EDTA concentration on the formation of the E* complex.
• To determine the optimal cation and concentration for E* formation.
• To elucidate the mechanism of C9gp fixation to EAC1-8hu.

Main Methods:

• Experiments were conducted using EAC1-8hu and C9gp in solutions with varying EDTA concentrations (0.09 M and 0.001 M).
• The effect of different divalent cations on E* formation was tested.
• The optimal concentration of the most effective cation was determined.

Main Results:

• E* formation was completely inhibited in 0.09 M EDTA.
• EAC1-8hu could not fix C9gp in 0.001 M EDTA.
• E* formation was observed in buffers with low concentrations of divalent cations.
• Calcium ions (Ca++) were the most effective, with an optimal concentration of 2 X 10(-7) M.

Conclusions:

• Divalent cations, particularly calcium, are essential for the formation of the E* complex.
• High concentrations of EDTA prevent E* formation by chelating necessary divalent cations.
• The optimal concentration of Ca++ for E* formation is very low, suggesting a specific regulatory role.