Research Article 7: The Activation of Mutant β-galactosidase by Specific Antibodies

Abstract

Immunological studies with wild-type and mutant β-galactosidase have been used for the investigation of the structure, activity and mode of synthesis of this enzyme. Antibodies directed against β-galactosidase precipitate but do not inactivate the enzyme (Cohn and Torriani, 1952). The distribution of antigenic sites to which precipitating antibodies are bound has been studied with a series of nonsense, missense and deletion mutants (Fowler and Zabin, 1968). Anti β-galactosidase serum has been found to activate latent enzyme. Enzyme activity in growing β-galactosidase polypeptide chains on ribosomes could be increased 2-fold by addition of anti β-galactosidase antibodies (Lederberg et al., 1964). A lac⁻ mutant has been described producing β-galactosidase crossreacting material which could be activated to enzyme activity by the addition of anti β-galactosidase antiserum. The activation, up to 550-fold above background, was proportional to the antibody concentration (Rotman and Celada, 1968).

Such mutants are of interest in two areas of research:

Further information about the structure and activity of β-galactosidase may be obtained by understanding the mechanism of this activation due to the binding of specific antibodies at its corresponding antigenic site.

Mutant proteins of this kind seem to be powerful tools in detecting antibodies against a specific antigenic determinant on a protein molecule. An assay for cells producing and secreting such antibodies seems possible. Antibody-like receptors on the surface of lymphoid cells, sensitive to this antigenic site, may be localized.

With these problems in mind, we have isolated eleven mutants producing an inactive β-galactosidase which is activated by...