THE ASSOCIATION OF THE SUBUNITS OF COMPONENT C3 OF HAGFISH COMPLEMENTIS UNSTABLE AND LEADS TO NOVEL DEGRADATION DURING ELECTROPHORESIS

An opsonic molecule that is designated the third component of hagfish complement (HC3), and a fragment of HC3 known as HC3b have recently be en identified in the hagfish, Eptatretus burgeri. These proteins were purified from plasma and generated a set of several bands and/or smear s during SDS-PAGE under standard, non-reducing conditions. Two-dimensi onal electrophoretic analysis of the proteins under nonreducing and re ducing conditions revealed the breakdown of polypeptides at the site o f a thioester bond and the concomitant partial release of a split prod uct, depending on the weak covalent or non-covalent association of pol ypeptide chains, in a large fraction of molecules of HC3 during SDS-PA GE. Moreover, the heterogeneity of HC3b can be ascribed to the differe nt configurations of subunits. A similar phenomenon was not observed i n the case of lamprey C3, even though breakdown of polypeptides at a t hioester bond did occur in some molecules.