Inhibition of human liver beta-galactosidases and beta-glucosidase by n-bromoacetyl-beta-D-galactosylamine

Area of Science:

• Biochemistry
• Enzymology
• Human Liver Physiology

Background:

• Beta-galactosidases are crucial lysosomal hydrolases involved in carbohydrate metabolism.
• Understanding enzyme inhibition mechanisms is key to developing targeted therapies.

Purpose of the Study:

• To investigate the inhibitory effects of N-Bromoacetyl-beta-D-galactosylamine on human liver beta-galactosidases.
• To explore the potential for this inhibitor to affect other lysosomal hydrolases, particularly beta-glucosidase.
• To determine if a single enzyme possesses both beta-galactosidase and beta-glucosidase activities.

Main Methods:

• Enzyme inhibition assays using N-Bromoacetyl-beta-D-galactosylamine.
• pH dependence studies of enzyme inactivation.
• Thermal inactivation studies at 52°C.
• Mixed-substrate experiments to assess enzyme specificity.

Main Results:

• N-Bromoacetyl-beta-D-galactosylamine irreversibly inhibits both acid and neutral beta-galactosidases.
• Inhibition of acid beta-galactosidase occurs at pKa = 4.5; neutral beta-galactosidase inhibition requires pH > 8.0.
• The inhibitor protects enzymes in the presence of substrates, indicating active site interaction.
• Neutral beta-glucosidase is also inactivated, with similar pH dependence and thermal stability as neutral beta-galactosidase.
• Mixed-substrate experiments support the existence of a single enzyme with both activities.

Conclusions:

• N-Bromoacetyl-beta-D-galactosylamine is a potent inhibitor of human liver beta-galactosidases.
• The data strongly suggest a single enzyme is responsible for both neutral beta-galactosidase and beta-glucosidase activities in human liver.
• This finding has implications for understanding lysosomal storage disorders and enzyme function.