Lysosomal beta-galactosidase from rat liver: purification, molecular forms and association with neuraminidase.

A simple procedure for purification of lysosomal beta-galactosidase from rat liver was developed. The association state of the purified enzyme has been found to depend on pH and ionic strength. Under acidic conditions and at high ionic strength, the enzyme is aggregated into a high molecular weight complex having a molecular weight of about 700,000. Increasing pH and lowering the ionic strength favour the disaggregation of the complex to an enzyme species whose molecular weight is 160,000. These two enzyme forms differ markedly in their hydrophobicity, but no significant differences in kinetic properties have been found. Galactose and galactose-1-amine were competitive inhibitors of beta-galactosidase. Neuraminidase is associated with the multimeric form of beta-galactosidase, whereas the low molecular weight form did not show any neuraminidase activity. The stability of neuraminidase has been found increase in the presence of magnesium ions.