MULTIPLE FORMS OF COMPLEMENT C3 IN TROUT THAT DIFFER IN BINDING TO COMPLEMENT ACTIVATORS

In all other species analyzed to date, the functionally active Term of complement component C3 exists as the product of a single gene. We ha ve now identified and characterized three functional C3 proteins (C3-1 , C3-3, and C3-4) in trout that are the products of at least two disti nct C3 genes. All three proteins are composed of an alpha- and a beta- chain and contain a thioester bond in the alpha-chain. However, they d iffer in their electrophoretic mobility, glycosylation, reactivity wit h monospecific C3 antibodies, and relative ability to bind to various surfaces (zymosan, Escherichia coli, erythrocytes). A comparison of th e partial amino acid sequences of the three proteins showed that the a mino acid sequence identified/similarity of C3-3 to C3-4 is 87/91%, wh ile that of C3-3 and C3-4 to C3-1 is 51.5/65.5% and 60/73% respectivel y. Thus, trout possess multiple forms of functional C3 that represent the products of several distinct genes and differ in their ability to bind covalently to various complement activators.