Activation of beta-galactosidase by monoclonal antibodies.

Four monoclonal cell lines secreting antibodies that activate the beta-galactosidase protein from lac-aba strains of Escherichia coli have been isolated. One of the antibodies, BG 79, inhibits the normal beta-galactosidase from E. coli in addition to its activation of the protein from mutants. Moreover, when in combination with any of the other activating antibodies, BG 79 exhibits synergistic activation of the beta-galactosidase protein, and the synergistically activated enzyme is stimulated by methanol, although most of the proteins activated by single antibodies are inhibited by methanol. The equilibrium of binding of BG 79 to the beta-galactosidase protein is not affected by the presence of a second antibody, and the half-time for activation by BG 79 is only slightly, though significantly, increased by preincubation of the protein with the second antibody. Our results imply that activation of beta-galactosidase proteins is not a simple correction of a conformational defect, and that many distinct active conformations are available to the enzyme.