Effects of thiol protease inhibitors on intracellular degradation of exogenous β-galactosidase in cultured human skin fibroblasts

The effects of low molecular weight (LMW) protease inhibitors of microbial origin were evaluated on the intracellular degradation of β-galactosidase purified from Aspergillus oryzae and taken up by cultured human skin fibroblasts with β-galactosidase deficiency. Only thiol protease inhibitors showed an effect to increase the enzyme activity. E-64, a specific inhibitor of thiol proteases, prolonged 3-fold a half life of the exogenous β-galactosidase and when the enzyme was supplied as liposomes, the half life was prolonged 9-fold in these cells. The role of thiol proteases in the degradation of enzyme molecules was discussed.