A cleavage product of mouse C3 adsorbable to (1----3)-beta-D-glucan from Alcaligenes faecalis var. myxogenes IFO 13140.

By using affinity chromatography of TAK, a gel-forming antitumor (1----3)-beta-D-glucan produced by Alcaligenes faecalis var. myxogenes IFO 13140 also known as an activator of the alternative complement pathway (ACP), we obtained from mouse serum a cleavage product of C3 (tentatively designated as C3X). Binding between C3X and TAK seemed to be noncovalent. In contrast to C3, C3X had an intact beta chain (70,000 daltons) and instead of an alpha chain, two peptide chains (40,000 and 30,000 daltons) linked by disulfide bonds. C3X retained a portion of C3 antigenicity. By trypsinolysis C3 yielded a fragment similar to C3X on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results suggest that C3X is C3c. Since C3X was obtained by elution with a high salt solution from TAK incubated with ethylenediaminetetraacetate (EDTA)-serum (serum containing EDTA) but not from TAK incubated with EDTA-plasma, C3X could already be present in the serum before the activation of ACP by TAK.