Human lactase and the molecular basis of lactase persistence

Area of Science:

• Biochemistry
• Molecular Biology
• Gastroenterology

Background:

• Human lactase is a key enzyme in lactose digestion.
• Lactase non-persistence is common in adults worldwide.
• Understanding lactase structure and regulation is crucial for digestive health.

Purpose of the Study:

• To characterize the purified human lactase enzyme.
• To investigate the relationship between lactase and phlorizin hydrolase.
• To explore the molecular basis of lactase persistence.

Main Methods:

• Monoclonal immunoadsorbent chromatography for lactase purification.
• Proteolytic treatment to yield hydrophilic enzyme variants.
• Enzyme activity assays and immunodiffusion techniques.

Main Results:

• Purified human lactase exists as a dimer of identical subunits.
• Proteolytic cleavage yields a hydrophilic enzyme.
• Lactase hydrolyzes lactose, cellobiose, and synthetic substrates, but not glucocerebroside.
• Phlorizin hydrolase activity is consistently associated with lactase.
• Adult and infant lactases are immunologically indistinguishable.
• Reduced lactase activity correlates with reduced cross-reacting material.

Conclusions:

• Lactase is a dimer composed of identical subunits.
• Phlorizin hydrolase is an integral component of the lactase complex.
• Lactase persistence is attributed to the continuous synthesis of the infant form of the enzyme.