The Requirement for Magnesium Ions in the Inactivation of the Third Component of Human Complement (C′3) by Insoluble Residues of Yeast Cells (Zymosan)

Abstract

Mg⁺⁺ is required for the inactivation of C′3 by insoluble residues of yeast cells (zymosan). The concentration of Mg⁺⁺ in normal serum is more than adequate for the reaction to proceed optimally. The requirement for Mg⁺⁺ is also demonstrated by the greater uptake of serum nitrogen by zymosan in the presence of Mg⁺⁺ than in its absence. The inactivation of human C′3 by zymosan appears to be a stoichiometric reaction sharply dependent on temperature, ionic strength and pH. The optimum conditions are at 37 C, ionic strength 0.15 or less, and pH 6.8–8.6. The complex formed upon the addition of zymosan to serum is highly undissociable or results in the destruction of C′3 activity. Attempts to elute C′3 from the zymosan complex were unsuccessful.