The Mechanism of Activation of Mutant β‐Galactosidase by Specific Antibodies

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Abstract
Measurements of the rates of activation of mutant β‐galactosidases of Escherichia coli by specific antibodies to enzyme activity suggest that the rate‐limiting step of this activation reaction is the mono‐molecular reaction, with which a mutant enzyme population changes between two conformations. Four mutant β‐galactosidases produced by one group of mutants all have an activation energy for this monomolecular reaction of 23.2 kcal/mol. Mutant enzyme‐activating antibodies appear to change the equilibrium between a wild‐type‐enzyme and a mutant‐enzyme conformation to more active molecules by stabilizing the wild‐type conformation. Different antisera activate one mutant enzyme population to different specific activities, all below that of the wild‐type enzyme.Activating antibodies can be enriched from antibodies with specificities against determinants on the enzyme by passage of antiserum over Sepharose‐mutant enzyme immunosorbent columns.