Isolation and functional effects of monoclonal antibodies binding to thymidylate synthase

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Abstract
Monoclonal antibodies against electrophoretically pure thymidylate synthase from HeLa cells were produced. Antibodies (M-TS-4 and M-TS-9) from hybridoma clones were shown by enzyme-linked immunoassay to recognize thymidylate synthase from a variety of human cell lines, but they did not bind to thymidylate synthase from mouse cell lines. The strongest binding of antibodies was observed to enzyme from HeLa cells. These 2 monoclonal antibodies bind simultaneously to different antigenic sites on thymidylate synthase purified from HeLa cells, as reflected by a high additivity index and results of cross-linked radioimmunoassay. Both mononclonal antibodies inhibit the activity of thymidylate synthase from human cell lines. The strongest inhibition was observed with thymidylate synthase from HeLa cells. Monoclonal antibody M-TS-9 (IgM subclass) decreased the rate of binding of [3H] Fd[fluorodeoxy]UMP to thymidylate synthase in the presence of 5,10-methylenetethydrofolate while M-TS-4 (IgG1) did not change the rate of ternary complex formation. The antibodies recognize different epitopes on the enzyme molecule.