The third component of complement: covalent attachment of a radioactive sugar to the labile binding site of C3 via the alternative pathway.

Journal Article (Journal Article)

A complement- (C) fixing particle consisting of agarose beads to which 5-thioglucose was attached by a --S--S-- bond (agarose-thioglucose) was employed to investigate the mechanism of attachment of C3 to surfaces. When whole serum containing [125I] C3 was incubated with agarose-thioglucose, labeled C3b was taken up in a form that was not removed by 2 M NaCl but was released by 10 mM dithiothreitol. Deposition of DTT-releasable C3b was dependent upon the alternative pathway of C activation. Gel electrophoresis of DTT-releasable C3b from similar experiments performed with unlabeled serum and agarose-[3H]thioglucose showed that the liberated C3b contained a molecule of radioactive thioglucose attached to the alpha'-chain by a covalent bond that was stable to mercaptoethanol. We propose that the thioglucose-alpha' chain bond was formed during the course of C activation by a reaction between the "labile binding site" of newly released C3b and the (then) particle-bound sugar. This formulation implies that the reaction by which C3b attaches to 5-thioglucose in this system is the reaction responsible for opsonization by C3b, and that the C3b-linked sugar represents a marker for the labile binding site. Incubation of the particle-bound C3b in serum resulted in the cleavage of the covalently linked alpha'-chain to several smaller polypeptides, the major cleavage product having a m.w. of 70,000.

Full Text

Duke Authors

Cited Authors

  • Mann, J; O'Brien, R; Hostetter, MK; Alper, CA; Rosen, FS; Babior, BM

Published Date

  • June 1981

Published In

Volume / Issue

  • 126 / 6

Start / End Page

  • 2370 - 2372

PubMed ID

  • 6785350

International Standard Serial Number (ISSN)

  • 0022-1767


  • eng

Conference Location

  • United States