Isolation and characterization of the third component of bovine complement

Area of Science:

• Immunology
• Biochemistry

Background:

• Complement component 3 (C3) is a central protein in the complement system.
• Understanding bovine C3 is crucial for comparative immunology and complement research.

Purpose of the Study:

• To isolate and characterize bovine complement component 3 (C3).
• To investigate the enzymatic properties and variants of bovine C3.

Main Methods:

• Purification of C3 using polyethylene glycol precipitation and multiple chromatography techniques (DEAE-Sephadex A-50, CM-Sephadex A-50, Sephacryl S-200).
• Analysis of molecular weight, cleavage products (C3a, C3b) via SDS-PAGE, and electrophoretic variants using isoelectric focusing.
• Functional assays involving purified bovine factors B and D to assess C3 convertase activity.

Main Results:

• Bovine C3 was purified, revealing a molecular weight of 183,000 Da (alpha-chain 114,000 Da, beta-chain 69,000 Da).
• Cleavage by a CVF-induced convertase yielded C3a (11,000 Da) and C3b (172,000 Da).
• At least three electrophoretic variants of C3 were identified (pI 6.55-6.85), and the isolated protein facilitated C3 convertase formation and function.

Conclusions:

• The study successfully isolated and characterized bovine C3, including its subunit composition and molecular weight.
• Bovine C3 exists in multiple electrophoretic forms and plays a key role in C3 convertase activity.
• The generated antiserum was specific for bovine C3, showing no cross-reactivity with human C3 or CVF.