Lactase-Phlorizin Hydrolase
Lactase
Epimedium
Phlorhizin
Lactose Intolerance
Hierarchy of sorting signals in chimeras of intestinal lactase-phlorizin hydrolase and the influenza virus hemagglutinin. (1/107)
Lactase-phlorizin hydrolase (LPH) is an apical protein in intestinal cells. The location of sorting signals in LPH was investigated by preparing a series of mutants that lacked the LPH cytoplasmic domain or had the cytoplasmic domain of LPH replaced by sequences that comprised basolateral targeting signals and overlapping internalization signals of various potency. These signals are mutants of the cytoplasmic domain of the influenza hemagglutinin (HA), which have been shown to be dominant in targeting HA to the basolateral membrane. The LPH-HA chimeras were expressed in Madin-Darby canine kidney (MDCK) and colon carcinoma (Caco-2) cells, and their transport to the cell surface was analyzed. All of the LPH mutants were targeted correctly to the apical membrane. Furthermore, the LPH-HA chimeras were internalized, indicating that the HA tails were available to interact with the cytoplasmic components of clathrin-coated pits. The introduction of a strong basolateral sorting signal into LPH was not sufficient to override the strong apical signals of the LPH external domain or transmembrane domains. These results show that basolateral sorting signals are not always dominant over apical sorting signals in proteins that contain each and suggest that sorting of basolateral from apical proteins occurs within a common compartment where competition for sorting signals can occur. (+info)Lactase-phlorizin hydrolase and sucrase-isomaltase genes are expressed differently along the villus-crypt axis of rat jejunum. (2/107)
Lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are two disaccharidases specifically expressed in small intestinal absorptive cells. We previously showed that the transcripts of both genes are elevated within 12 h of carbohydrate intake. To examine at which locus of villus-crypt axis this response to dietary carbohydrate occurs, 6-wk-old rats were fed a low-carbohydrate diet (5% energy) for 7 d, and then force-fed either the low-carbohydrate diet or a sucrose (40% energy) diet during the last 6 h. Cryostat sectioning of jejunal segments followed by RNA blot hybridizations of the transcripts revealed that, unlike SI mRNA which was expressed maximally in the lower villus, maximal LPH mRNA level was attained at the upper villus. The distribution of the respective immunoreactive protein and the enzymatic activity was shifted more toward the villus tips for LPH than for SI. Force-feeding the sucrose diet caused an abrupt increase in SI mRNA level in the lower villus within 3 h, while the rise in LPH mRNA level occurred in the mid- and upper-villus. The diet-induced increases in the LPH mRNA and SI mRNA levels were abolished along the entire villus by the administration of actinomycin D. These results suggest that LPH gene is maximally expressed in more apical villus cells than SI gene, and that dietary sucrose elicits enhancement of the gene expressions in the villus cells which are accumulating the respective transcripts. (+info)Requirement for a different hydrophobic moiety and reliable chromogenic substrate for endo-type glycosylceramidases. (3/107)
A series of synthetic lactosides with aglycones that differed in length and structure were used to determine the substrate specificity of endo-type glycosylceramidases. Endoglycoceramidases (EGCase) from bacteria preferred lactosides with an acylamide structure over simple n-alkyl lactosides. While ceramide glycanase (CGase) from leech did not show preference. N -Acylaminoethyl beta-lactosides and n -alkyl lactosides were substrates for both EGCase and CGase, but N-acylaminobutyl beta-lactosides, whose acylamide residue differs from that in ceramide, were not hydrolyzed by EGCases. Thus, EGCases, but not CGase, appear to require an N-acyl group at the same position as that of intact glycosphingolipid for substrate recognition. A p-nitrophenyl lactoside derivative possessing an N-acyl chain was degraded by both EGCases and CGase and this chromogenic substrate may be an alternative substrate for endo-type glycosylceramidase activity. Km of the chromogenic lactoside for CGase and Rhodococcus EGCase were 28 microM and 2.9 mM, respectively. (+info)Species differences in the sites of cleavage of pro-lactase to lactase supports lack of selective pressure. (4/107)
The pro-sequences in pro-lactase-phlorizin hydrolase (LPH) are needed for lactase to proceed past the ER, but are irrelevant as to the enzymatic activities. Hence, in all species removal of the pro- sequences (or most of them) must take place after the ER. Contrary to this, the details of the removal of these pro-sequences are to be expected to differ in the various species, since they are not subjected to selective pressure. Using site-directed mutagenesis we investigated processing in rabbit. The first cleavage occurs by furin (or furin-like PCs) and takes place at R-A-A-R(349) in the pro-sequence, generating the known 180 kDa intermediate. Replacing R(349) by Q results in a mutant which is not cleaved but nevertheless transported to the cell surface as demonstrated by immunofluorescence. Further processing of either the 180 kDa intermediate or the mutant is not directly mediated by furin-like PCs, but involves (also) other proteases. These results demonstrate that formation of the 180 kDa intermediate, consistently found only in rabbits, but not in man, is not essential for lactase transport: in all likelihood lack of selective pressure has led to species-specific processing of pro-LPH. (+info)Interaction between the homeodomain proteins Cdx2 and HNF1alpha mediates expression of the lactase-phlorizin hydrolase gene. (5/107)
Lactase-phlorizin hydrolase is a brush-border enzyme which is specifically expressed in the small intestine where it hydrolyses lactose, the main carbohydrate found in milk. We have previously demonstrated in transgenic mice that the tissue-specific and developmental expression of lactase is controlled by a 1 kb upstream region of the pig lactase gene. Two homeodomain transcription factors, caudal-related homeodomain protein (Cdx2) and hepatic nuclear factor 1alpha (HNF1alpha), are known to bind to regulatory cis elements in the promoters for several intestine-specific genes, including lactase, and are present in mammalian intestinal epithelia from an early stage in development. In the present study, we examined whether Cdx2 and HNF1alpha physically interact and co-operatively activate transcription from the lactase-phlorizin hydrolase promoter. We show that the presence of both factors leads to a much higher level of transcription than the sum of the activation by either factor alone. The N-terminal activation domain of Cdx2 is required for maximal synergy with HNF1alpha. With the use of pull-down assays, we demonstrate a direct protein-protein interaction between Cdx2 and HNF1alpha. The interaction domain includes the homeodomain region of both proteins. This is the first demonstration of a functional interaction between two transcription factors involved in the activation of a number of intestine-specific genes. Synergistic interaction between tissue-restricted factors is likely to be an important mechanism for reinforcing developmental and tissue-specific gene expression within the intestine. (+info)Dietary flavonoid and isoflavone glycosides are hydrolysed by the lactase site of lactase phlorizin hydrolase. (6/107)
Lactase phlorizin hydrolase (LPH; EC 3.2.1.62) is a membrane-bound, family 1 beta-glycosidase found on the brush border of the mammalian small intestine. LPH, purified from sheep small intestine, was capable of hydrolysing a range of flavonol and isoflavone glycosides. The catalytic efficiency (k(cat)/K(m)) for the hydrolysis of quercetin-4'-glucoside, quercetin-3-glucoside, genistein-7-glucoside and daidzein-7-glucoside was 170, 137, 77 and 14 (mM(-1) s(-1)) respectively. The majority of the activity occurred at the lactase and not phlorizin hydrolase site. The ability of LPH to deglycosylate dietary (iso)flavonoid glycosides suggests a possible role for this enzyme in the metabolism of these biologically active compounds. (+info)Additional N-glycosylation and its impact on the folding of intestinal lactase-phlorizin hydrolase. (7/107)
Lactase-phlorizin hydrolase (LPH) is a membrane bound intestinal hydrolase, with an extracellular domain comprising 4 homologous regions. LPH is synthesized as a large polypeptide precursor, pro-LPH, that undergoes several intra- and extracellular proteolytic steps to generate the final brush-border membrane form LPHbeta(final). Pro-LPH is associated through homologous domain IV with the membrane through a transmembrane domain. A truncation of 236 amino acids at the COOH terminus of domain IV (denoted LAC236) does not significantly influence the transport competence of the generated mutant LPH1646MACT (Panzer, P., Preuss, U., Joberty, G., and Naim, H. Y. (1998) J. Biol. Chem. 273, 13861-13869), strongly suggesting that LAC236 is an autonomously folded domain that links the ectodomain with the transmembrane region. Here, we examine this hypothesis by engineering several N-linked glycosylation sites into LAC236. Transient expression of the cDNA constructs in COS-1 cells confirm glycosylation of the introduced sites. The N-glycosyl pro-LPH mutants are transported to the Golgi apparatus at substantially reduced rates as compared with wild-type pro-LPH. Alterations in LAC236 appear to sterically hinder the generation of stable dimeric trypsin-resistant pro-LPH forms. Individual expression of chimeras containing LAC236, the transmembrane domain and cytoplasmic tail of pro-LPH and GFP as a reporter gene (denoted LAC236-GFP) lends strong support to this view: while LAC236-GFP is capable of forming dimers per se, its N-glycosyl variants are not. The data strongly suggest that the LAC236 is implicated in the dimerization process of pro-LPH, most likely by nucleating the association of the ectodomains of the enzyme. (+info)Differential mechanism-based labeling and unequivocal activity assignment of the two active sites of intestinal lactase/phlorizin hydrolase. (8/107)
Milk lactose is hydrolysed to galactose and glucose in the small intestine of mammals by the lactase/phlorizin hydrolase complex (LPH; EC 3.2.1.108/62). The two enzymatic activities, lactase and phlorizin hydrolase, are located in the same polypeptide chain. According to sequence homology, mature LPH contains two different regions (III and IV), each of them homologous to family 1 glycosidases and each with a putative active site. There has been some discrepancy with regard to the assignment of enzymatic activity to the two active sites. Here we show differential reactivity of the two active sites with mechanism-based glycosidase inhibitors. When LPH is treated with 2',4'-dinitrophenyl 2-deoxy-2-fluoro-beta-D-glucopyranoside (1) and 2', 4'-dinitrophenyl-2-deoxy-2-fluoro-beta-D-galactopyranoside (2), known mechanism-based inhibitors of glycosidases, it is observed that compound 1 preferentially inactivates the phlorizin hydrolase activity whereas compound 2 is selective for the lactase active site. On the other hand, glycals (D-glucal and D-galactal) competitively inhibit lactase activity but not phlorizin hydrolase activity. This allows labeling of the phlorizin site with compound 1 by protection with a glycal. By differential labeling of each active site using 1 and 2 followed by proteolysis and MS analysis of the labeled fragments, we confirm that the phlorizin hydrolysis occurs mainly at the active site located at region III of LPH and that the active site located at region IV is responsible for the lactase activity. This assignment is coincident with that proposed from the results of recent active-site mutagenesis studies [Zecca, L., Mesonero, J.E., Stutz, A., Poiree, J.C., Giudicelli, J., Cursio, R., Gloor, S.M. & Semenza, G. (1998) FEBS Lett. 435, 225-228] and opposite to that based on data from early affinity labeling with conduritol B epoxide [Wacker, W., Keller, P., Falchetto, R., Legler, G. & Semenza, G. (1992) J. Biol. Chem. 267, 18744-18752]. (+info)Lactase-phlorizin hydrolase (LPH) is an enzyme that is primarily responsible for the digestion of lactose, a sugar found in milk and dairy products. LPH is located on the brush border of the small intestine and catalyzes the hydrolysis of lactose into its component sugars, glucose and galactose, which are then absorbed into the bloodstream.
LPH is also known as lactase, and a deficiency in this enzyme can lead to a condition called lactose intolerance. In lactose intolerance, the body is unable to properly digest lactose, leading to symptoms such as bloating, diarrhea, and abdominal cramps.
Phlorizin is a compound that was originally used in research to study the properties of LPH. It is not typically associated with the physiological function of this enzyme in the body.
Lactase is a specific enzyme that is produced by the cells lining the small intestine in humans and other mammals. Its primary function is to break down lactose, a sugar found in milk and dairy products, into simpler sugars called glucose and galactose, which can then be absorbed into the bloodstream.
Lactase is most active during infancy and early childhood, when breast milk or formula is the primary source of nutrition. However, in some individuals, lactase production decreases after weaning, leading to a condition called lactose intolerance. Lactose intolerant individuals have difficulty digesting lactose, which can result in various gastrointestinal symptoms such as bloating, cramps, diarrhea, and gas.
Supplemental lactase enzymes are available over the counter to help lactose-intolerant individuals digest dairy products more comfortably.
Epimedium is a genus of plants in the family Berberidaceae, also known as barberry family. It is commonly known as Horny Goat Weed due to its traditional use as an aphrodisiac in Chinese medicine. The active compound of Epimedium, icariin, has been studied for its potential effects on improving sexual function and treating erectile dysfunction. However, more research is needed to confirm these findings and establish the safety and efficacy of this herb as a treatment for sexual dysfunction.
It's important to note that natural does not always mean safe, and it's crucial to consult with a healthcare provider before starting any new supplement regimen, including Epimedium, to ensure safety and avoid potential interactions with other medications.
Phlorhizin is not a medical condition or term, but rather a chemical compound. It is a glucoside that can be found in the bark of apple trees and other related plants. Phlorhizin has been studied in the field of medicine for its potential effects on various health conditions. Specifically, it has been shown to inhibit the enzyme called glucose transporter 2 (GLUT2), which is involved in the absorption of glucose in the body. As a result, phlorhizin has been investigated as a potential treatment for diabetes, as it may help regulate blood sugar levels. However, more research is needed to fully understand its effects and safety profile before it can be used as a medical treatment.
Lactose intolerance is a digestive condition in which the body has difficulty digesting lactose, a sugar found in milk and dairy products. This occurs due to a deficiency or insufficiency of lactase, an enzyme produced by the small intestine that breaks down lactose into simpler sugars (glucose and galactose) for absorption. When there is not enough lactase to digest the consumed lactose, it passes undigested into the large intestine, where it is fermented by bacteria, leading to various gastrointestinal symptoms.
The symptoms of lactose intolerance may include bloating, cramps, diarrhea, nausea, and gas, usually occurring within 30 minutes to two hours after consuming dairy products. The severity of these symptoms can vary depending on the amount of lactose consumed and an individual's level of lactase deficiency or insufficiency.
Lactose intolerance is not life-threatening but can cause discomfort and may affect a person's quality of life. It is essential to manage the condition through dietary modifications, such as consuming smaller amounts of dairy products, choosing lactose-free or reduced-lactose options, or using lactase enzyme supplements before eating dairy products. In some cases, a healthcare professional may recommend additional management strategies based on an individual's specific needs and medical history.