Agglutinating activities of the subunits of one igm cold agglutinin treated with various reducing agents

A single 19 S IgM cold agglutinin was reduced with various agents. The agglutinating activity of such subunits and of reaggregation polymers was measured in a Technicon Autoanalyzer, using two different techniques. Preservation of intra‐ and interchain disulfide bridges is essential for agglutinating activity. Excess 2‐mercaptoethanol destroyed this activity almost totally, whereas subunits obtained with 0.02 M cysteine retained the highest degree of activity. Subunits obtained with dithiothreitol also retained appreciable activity, although their interchain disulfide bonds were destroyed. Subunits prepared with mercaptoethylamine exhibited weak activity, which may be due to the disulfide bonds' being broken in one of the two μ‐light chain pairs. The tridimensional structure and polymeric form of the molecule are essential factors, since noncovalent polymers always had a higher activity than their subunits. Reoxidation of nonalkylated subunits prepared by cysteine recovered 75 % of the native IgM activity.