The biosynthetic basis of adult lactase deficiency.
نویسندگان
چکیده
The intestinal brush-border enzyme lactase splits lactose into its component monosaccharides, glucose and galactose. Relative deficiency of the enzyme during adulthood is a common condition worldwide and is frequently associated with symptoms of lactose intolerance. We studied the synthesis and processing of lactase in normal and adult hypolactasic subjects using human intestinal explants in organ culture. Metabolic labeling experiments in our control subjects with [35S]methionine followed by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, and fluorography demonstrated that newly synthesized lactase is initially recognized as a precursor molecule with a relative molecular weight (Mr) of 205,000. Over the course of several hours most of the labeled lactase was converted to a mature form of 150,000 Mr. Transiently appearing forms of 215,000 and 190,000 Mr were identified and were felt to represent intermediary species generated during intracellular processing. We identified two distinct alterations in lactase biosynthesis accounting for adult hypolactasia. Studies in three deficient subjects demonstrated markedly reduced synthesis of the precursor protein though posttranslational processing appeared identical to normal. Multiple studies in a fourth deficient subject demonstrated synthesis of ample amounts of precursor lactase but reduced conversion to the mature active form of the enzyme.
منابع مشابه
Evaluation of a Genetic Test for Diagnose of Primary Hypolactasia in Northeast of Iran (Khorasan)
Objective(s) Primary or adult type hypolactasia, the most common enzyme deficiency in the world, is due to reduced lactase activity in the intestinal cell after weaning. Lactase non-persistence is inherited as an autosomal recessive trait. A DNA variant, single nucleotide polymorphism C/T−13910 which is located on 13910 base pairs (bp) upstream of the lactase gene (LCT) at chromosome 2 has been...
متن کاملMolecular Genetics of Lactase Persistence
This thesis is based on the following original articles, which are referred to in the text by their Roman numerals. In addition, some unpublished data are presented Assignment of the locus for congenital lactase deficiency to 2q21, in the vicinity of but separate from the lactase-phlorizin hydrolase gene. Identification of a variant associated with adult-type hypolactasia. Transcriptional regul...
متن کاملMolecular and cellular aspects and regulation of intestinal lactase-phlorizin hydrolase.
Carbohydrates are hydrolyzed in the intestinal lumen by specific enzymes to monosaccharides before transport across the brush border membrane of epithelial cells into the cell interior. The enzymes implicated in the digestion of carbohydrates in the intestinal lumen are membrane-bound glycoproteins that are expressed at the apical domain of the enterocytes. Absent or reduced activity of one of ...
متن کاملHypolactasia: a common enzyme deficiency leading to lactose malabsorption and intolerance.
Adult‑type hypolactasia (lactase nonpersistence or lactase deficiency) is the most common enzyme deficiency leading to lactose intolerance and primary lactose malabsorption. Clinical presentation of the condition includes symptoms resulting from bacterial fermentation of undigested lactose in the colon, which gives rise to gas bloat, increased motility, and loose stools. Diagnosis of the diseas...
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ورودعنوان ژورنال:
- The Journal of clinical investigation
دوره 86 4 شماره
صفحات -
تاریخ انتشار 1990