title: Human lactase and the molecular basis of lactase persistence.
abstract: 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 (160K). 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-beta-galactoside and beta-glucoside, as well as phlorizin; but it does not hydrolyze glucocerebroside. Phlorizin hydrolase is associated with lactase 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.
mesh_terms: D000911:Antibodies, Monoclonal; D002846:Chromatography, Affinity / Q000379:methods; D005696:Galactosidases / Q000235:genetics*; D006023:Glycoproteins / Q000032:analysis; D006801:Humans; D005779:Immunodiffusion; D007123:Immunoelectrophoresis, Two-Dimensional; D007583:Jejunum / Q000201:enzymology; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D006023:Glycoproteins; D005696:Galactosidases; D001616:beta-Galactosidase