title: The nature of small bowel luminal fluid lactase.
abstract: The evidence indicating a mucosal source for the jejunal fluid lactase activity of children is so far inconclusive. Samples of jejunal mucosa and the adjacent fluid were obtained simultaneously from 15 children. Lactase activity was measured at pH 5.9 in mucosa and fluid. Fluid activities showed a significant positive correlation with the activity of the corresponding mucosal homogenate but a stronger correlation was found with an enterocyte microvillous membrane fraction prepared from the same homogenate (r = 0.807 and 0.889, respectively). Kinetic and pH optima studies were consistent with a microvillous membrane origin. Fluid activity and pH optimum were not changed detectably when measured in the presence of an enterocyte lysosomal acid lactase inhibitor. Jejunal fluid lactase activity and its properties closely reflect the microvillous membrane enzyme. Lysosomal acid lactase does not contribute measurably to the total lactase activity of jejunal fluid.
authors.affiliation: Department of Paediatrics, National University Hospital, Singapore.
authors.forename: S H
authors.initials: SH
authors.lastname: Quak
authors.forename: G A
authors.initials: GA
authors.lastname: Brown
authors.forename: I W
authors.initials: IW
authors.lastname: Booth
authors.forename: A S
authors.initials: AS
authors.lastname: McNeish
mesh_terms: D000293:Adolescent; D001826:Body Fluids / Q000201:enzymology*; D002648:Child; D002675:Child, Preschool; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007223:Infant; D007413:Intestinal Mucosa / Q000201:enzymology*; D007583:Jejunum / Q000201:enzymology*; D007700:Kinetics; D043322:Lactase; D008247:Lysosomes / Q000201:enzymology; D008871:Microvilli / Q000201:enzymology; D001616:beta-Galactosidase / Q000378:metabolism*
chemical_list: D043322:Lactase; D001616:beta-Galactosidase