Reversible Aggregation and Stability of Lysosomal Acid β-Galactosidase from Porcine Adrenal Cortex

Abstract

1. Acid β-galactosidase [EC 3. 2. 1. 23] of porcine adrenocortical lysosomes, assayed for its activity towards p-nitrophenyl-β-D-galactopyranoside, showed two activity peaks on gel filtration profile at pH 7.4, one corresponding to a molecular weight of approximately 270, 000 (termed form A 3) and the other about 65, 000 (termed form A 1).
2. Another form of acid β-galactosidase with a molecular weight of about 130, 000 (termed form A 2) was found when the high speed extract or partially purified form A 1 was chromatographed on Sephadex G-150 at pH 4.5.
3. In the presence of 0.1M NaCl or saturating amounts of substrate at pH 4.5, the high speed extract showed the aggregation of form A 2 yielding form A 3. Dissociation of form A 3 back to form A 1 was observed on incubation at 37°C in 0.02M sodium phosphate buffer, pH 7.4, and that was followed by irreversible enzyme inactivation.
4. Dissociation of form A 3 into form A 1 and enzyme inactivation in phosphate buffer, pH 7.4, were prevented by addition of 0.1M NaCl.
5. The interconvertible enzymic forms showed the same pH-activity profiles and Michaelis constants.
6. These results suggest that the lysosomal acid β-galactosidase in the porcine adrenal cortex exists in vivo as the dimer, and that the dimer may further aggregate into the tetramer.