Human lactase and the molecular basis of lactase persistence

✍ Scribed by Jennifer Potter; Mae-Wan Ho; Hilary Bolton; Anna J. Furth; Dallas M. Swallow; Beatrice Griffiths

• Publisher: Springer
• Year: 1985
• Tongue: English
• Weight: 827 KB
• Volume: 23
• Category: Article
• ISSN: 0006-2928
• DOI: 10.1007/bf00499084

✦ Synopsis

Human lactase purified from detergent extracts of the total membrane fraction of postmortem jejunum by means of monoclonal immunoadsorbent chromatography appears to be a dimer of subunits identical in Mr (16OK).

Trypsin or papain removes a small hydrophobic anchoring peptide from each subunit to give a hydrophilic enzyme which no longer interacts with detergent micelles. Lactase hydrolyzes, besides lactose, cellobiose and the synthetic substrates, 4-methylumbelliferyl-~-galactoside and fl-glucoside, as well as phlorizin; but it does not hydrolyze glucocerebroside. Phlorizin hydrolase is associated with laetase under all conditions investigated," coincident staining on immunodiffusion and immunoelectrophoresis, coincident elution on immunoadsorbent chromatography and on gel filtration in a dissociating buffer, and correlated reduction in activity in lactase-nonpersistent individuals. Adult and infant lactases are indistinguishable by titration or immunodiffusion against polyclonal rabbit antibodies. Adult individuals low in lactase activity also show a corresponding reduction in cross-reacting material. These observations suggest that lactase persistence is due to the continued synthesis of the infant enzyme.