Antibody-mediated thermal stabilization of human hexosaminidases.

Abstraet--N-Acetyl-hexosaminidase (Hex) exists in various human tissues in two major isozymic forms--Hex A and Hex B. The main difference between the two forms is the lability of Hex A to both heat and acid as compared to the stability of Hex B. When heated to 50°C for 2-3 hr Hex A loses its entire enzymatic activity. In the present study we demonstrate that specific antiserum stabilizes Hex A to heat inactivation. When maintained at 50°C for 3 hr in the presence of antibodies the enzyme retains up to 80 per cent of its original activity. This phenomenon is dependent on antibody concentration, and reaches its maximal value at the equivalence zone of Ag-Ab interaction. The inactivation is temperature-dependent; a shift of 12°C was observed in the midpoint of heat inactivation between the native and antibody-bound enzyme. A similar shift was observed for Hex B. Hex A was stabilized also by Hex A-specific antibodies which do not crossreact with Hex B. These findings indicate that the antibodies act as stabilizers of the active conformation of hexosaminidases.