The isolation and structure of C4, the fourth component of human complement

Area of Science:

• Biochemistry
• Immunology
• Proteomics

Background:

• The complement system is a crucial part of innate immunity.
• Complement component C4 (C4) plays a vital role in complement activation pathways.
• Understanding C4's structure is essential for elucidating its function.

Purpose of the Study:

• To isolate and characterize the peptide chains of human complement component C4.
• To determine the molecular weights, amino acid composition, and N-terminal sequences of C4's subunits.
• To provide detailed analytical data for human C4.

Main Methods:

• Isolation of C4 from human serum.
• Preparative methods for separating alpha, beta, and gamma peptide chains.
• Analysis of peptide chain molecular weights (apparent mol.wts.).
• Amino acid analysis and carbohydrate content determination.
• N-terminal amino acid sequencing.

Main Results:

• Human C4 was isolated in good yield from serum.
• C4 comprises three peptide chains: alpha (90,000 Da), beta (80,000 Da), and gamma (30,000 Da).
• Carbohydrate content: C4 (7.0%), alpha-chain (8.6%), beta-chain (5.6%).
• N-terminal sequences determined: 12 residues (alpha), 8 residues (beta), 19 residues (gamma).

Conclusions:

• The study successfully isolated and characterized the peptide chains of human C4.
• Detailed biochemical data on C4 subunits were provided.
• This characterization aids in understanding C4's role in the complement system.