Purification and properties of trehalase from rat intestinal mucosal cells

Gastrointestinal Function

This chapter describes the normal biochemical processes of intestinal secretion, digestion, and absorption. The digestive system is composed of the gastrointestinal (GI) tract, or the alimentary canal, salivary glands, the liver, and the exocrine pancreas. The principal functions of the gastrointestinal tract are to digest and absorb ingested nutrients, and to excrete waste products of digestion. Most nutrients are ingested in a form that is either too complex for absorption or insoluble, and therefore, indigestible or incapable of being digested. Within the GI tract, much of these substances are solubilized and further degraded enzymatically to simple molecules, sufficiently small in size, and in a form that permits absorption across the mucosal epithelium. This chapter explains in detail the mechanisms of salivary secretions, compositions of saliva, and the functions of saliva. The chapter also elaborates properties of bile as well as the synthesis of bile acids. The chapter explores the pathogenesis of the important gastrointestinal diseases of domestic animals, and the biochemical basis for their diagnosis and treatment. The chapter concludes with a discussion on disturbances of gastrointestinal function such as vomition, acute diarrheas, malabsorption, bacterial overgrowth, and ulcerative colitis.

Trehalose metabolism genes in Caenorhabditis elegans and filarial nematodes

The sugar trehalose is claimed to be important in the physiology of nematodes where it may function in sugar transport, energy storage and protection against environmental stresses. In this study we investigated the role of trehalose metabolism in nematodes, using Caenorhabditis elegans as a model, and also identified complementary DNA clones putatively encoding genes involved in trehalose pathways in filarial nematodes. In C. elegans two putative trehalose-6-phosphate synthase (tps) genes encode the enzymes that catalyse trehalose synthesis and five putative trehalase (tre) genes encode enzymes catalysing hydrolysis of the sugar. We showed by RT-PCR or Northern analysis that each of these genes is expressed as mRNA at all stages of the C. elegans life cycle. Database searches and sequencing of expressed sequence tag clones revealed that at least one tps gene and two tre genes are expressed in the filarial nematode Brugia malayi, while one tps gene and at least one tre gene were identified for Onchocerca volvulus. We used the feeding method of RNA interference in C. elegans to knock down temporarily the expression of each of the tps and tre genes. Semiquantitative RT-PCR analysis confirmed that expression of each gene was silenced by RNA interference. We did not observe an obvious phenotype for any of the genes silenced individually but gas-chromatographic analysis showed >90% decline in trehalose levels when both tps genes were targeted simultaneously. This decline in trehalose content did not affect viability or development of the nematodes.

Cloning, characterization and mapping of the mouse trehalase (Treh) gene

Trehalase is the least studied of the membrane-bound alpha- glucosidase enzymes. Here we report the isolation and characterization of the mouse trehalase (Treh) gene. Initially, PCR using primers based on published rat cDNA sequence was used to clone a partial mouse cDNA. This allowed design of mouse primers which identified a single positive clone in a bacterial artificial chromosome (BAC) library of mouse genomic DNA. Analysis of BAC subclones showed that the Treh structural gene spans approximately 13 kb and comprises 15 exons. Data from genomic Southern blotting were consistent with mouse Treh being a single copy gene. The transcription initiation site was determined by both S1 nuclease mapping and 5' rapid amplification of cDNA ends (5' RACE) to be located 25 nt upstream of the ATG in exon 1. The mouse Treh exons were found to have an open reading frame of 1728 nt and the encoded protein of 576 amino acids showed 81, 82 and 93% amino acid sequence identity with rabbit, human and rat trehalase, respectively. The trehalase signature sequence found at amino acids 162 to 175 had 100% identity with the corresponding region of rabbit, human and rat and 79% identity with that for yeast trehalase. When a mouse Treh cDNA was used for Northern blot analysis of RNA from 12 mouse tissues, Treh mRNA expression was detected only in kidney and small intestine. The size of the mRNA in both of these tissues was estimated to be approximately 2.1 kb, furthermore both tissues appear to have the same transcription initiation site as determined by nuclease protection. Using the T31 radiation hybrid panel, mouse Treh was shown to be located on Chromosome 9 in a broad region that is orthologous with human Chromosome 11q23. The human trehalase gene (TREH) was identified in the latter location via database searching, which also revealed the overall structure of the human gene as being similar to that of the mouse.

Rat trehalase: cDNA cloning and mRNA expression in adult rat tissues and during intestinal ontogeny

A partial rat trehalase cDNA has been cloned and used to examine trehalase mRNA expression. Northern blotting with total RNA from 11 adult rat tissues showed a trehalase transcript only in small intestine, where it was abundant in proximal regions but declined steeply toward the ileum. During development, trehalase mRNA was not detectable in jejunum until postnatal day 19 and then increased markedly through day 25. Modest levels in trehalase mRNA were induced precociously by administration of dexamethasone, with increasing responsiveness evident between the first and second postnatal weeks. In contrast, analysis of sucrase-isomaltase mRNA on the same blots showed maximal induction at both ages. In adrenalectomized animals, the ontogenic increase of trehalase mRNA began as usual but proceeded more slowly than in control animals. Overall, trehalase mRNA expression in the rat displayed both similarities and differences compared with rabbit. Moreover, the differences revealed in glucocorticoid responsiveness of trehalase mRNA and sucrase-isomaltase mRNA suggest that the actions of these hormones on the developing intestine may be more complex than previously recognized.

Influence of hydrocortisone acetate on pancreas and mucosal weight, amylase and disaccharidase activities in 14-day-old pigs

1. One litter of 12 pigs was used to evaluate the effects of hydrocortisone acetate injection on organ weight and carbohydrase activities. 2. Pigs were injected with hydrocortisone acetate or an equal volume of saline at 7 days of age and killed at 14 days, and tissues were collected, weighted, and analyzed for carbohydrase activities. 3. Hydrocortisone had no effect (P greater than 0.40) on daily gain, liver weight, spleen weight, or small intestinal length. 4. Hydrocortisone increased pancreatic weight by 29% and total pancreatic alpha-amylase content by 38%. 5. Hydrocortisone increased duodenal mucosal weight by 23%, duodenal lactase activity by 44%, duodenal maltase activity by 163%, and duodenal sucrase activity by 214%.

Rat intestinal trehalase. Studies of the active site

Rat intestinal trehalase was solubilized, purified and reconstituted into proteoliposomes. With octyl glucoside as the solubilizing detergent, the purified protein appeared as a single band on SDS/polyacrylamide-gel electrophoresis with an apparent molecular mass of 67 kDa. Kinetic studies indicated that the active site of this enzyme can be functionally divided into two adjacent regions, namely a binding site (with pKa 4.8) and a catalytic site (with pKa 7.2). Other findings suggested that the catalytic site contains a functional thiol group, which is sensitive to inhibition by N-ethylmaleimide, Hg2+ and iodoacetate. Substrate protection and iodoacetate labelling of the thiol group demonstrated that only a protein of 67 kDa was labelled. Furthermore, sucrose and phlorizin protected the thiol group, but Tris-like inhibitors did not. Structure-inhibition analysis of Tris-like inhibitors, the pH effect of Tris inhibition and Tris protection of 1-(3-dimethylaminopropyl)-3-ethylcarbodi-imide inactivation permitted characterization and location of a separate site containing a carboxy group for Tris binding, which may also be the binding region. On the basis of these findings, a possible structure for the active site of trehalase is proposed.

Purification and properties of detergent-solubilized pig kidney trehalase

Trehalase (alpha, alpha-trehalase, EC 3.2.1.28) was solubilized from the brush border membrane of pig kidney cortex by Triton X-100 and sodium deoxycholate in the presence of inhibitors of proteolytic enzymes. The kidney enzyme was purified 3060-fold using gel filtration, ion exchange chromatography, Con A-Sepharose chromatography, phenyl-Sepharose CL-4B hydrophobic interaction chromatography, Tris-Sepharose 6B affinity chromatography, and hydroxylapatite chromatography. Tris-Sepharose 6B was utilized to absorb contaminant proteins. Purity was estimated as 99% or greater, based on amino-terminal amino acid analysis. The purified enzyme had a specific activity of 278 units/mg protein, showed one major band after silver staining, and had an estimated molecular weight of 80,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme was a glycoprotein and contained 2 mol of glucosamine per mole of trehalase. Kidney trehalase was inhibited by Tris, HgCl2, and phlorizin with Ki values of 3.8 mM, 11 microM, and 2.4 mM, respectively. Inclusion of Cl- in the reaction mixture protected the enzyme from inactivation by HgCl2. The apparent Km for trehalose was calculated to be 2.1 mM. Kidney trehalase was highly specific for trehalose and exhibited an optimal pH of 5.9. The isoelectric point was between pH 4.7 and 4.4, as measured by chromatofocusing.

Intestinal and renal origin of trehalase activity in rabbit amniotic fluid

To utilize specific fetal markers in amniotic fluid for prenatal detection of fetal anomalies, it is necessary to determine the precise tissue origin of these markers. In rabbit fetuses, we distinguished between intestinal and renal forms of trehalase (alpha,alpha'-trehalose-1-D-glucohydrolase, EC 3.2.1.28) in amniotic fluid on the basis of differences in net electric charges. Trehalase was solubilized from purified brush-border membranes of fetal rabbit kidney and intestine by Triton X-100 treatment, whereas the trehalase activity in amniotic fluid was soluble. The kinetic properties of trehalase from intestine, kidney and amniotic fluid were very similar. The Mr of the soluble amniotic fluid trehalase was between 72,600 and 66,300 from hydrodynamic parameters, depending on the amount of sugar bound to the enzyme, and 48,500 by radiation inactivation, a method which detects only the protein part of the enzyme. For membrane-bound trehalase from kidney and intestine in situ the radiation inactivation method also gave a molecular size of around 49,000. Isoelectric focusing of freshly solubilized membranes allowed us to distinguish between renal and intestinal forms of trehalase in rabbit fetuses on the basis of different isoelectric points. Each trehalase form was also present in the amniotic fluid but in varying proportions depending on the gestational age at which the amniotic fluid was collected. The results suggest that early in gestation amniotic fluid trehalase activity originates exclusively from the fetal kidney but that more and more intestinal enzyme is released into the amniotic cavity as the fetus develops. Similar results were also obtained when ion-exchange chromatography was used to separate the various trehalase forms. The development of trehalase activity in rabbit fetal kidney and intestine correlates well with its occurrence in the amniotic fluid; trehalase activity in the kidney develops early in gestation whereas the intestinal trehalase activity develops just before term.

4-Aminobutyrate:2-oxoglutarate aminotransferase from Candida. Purification and properties

An enzyme which catalyzes the transamination of 4-aminobutyrate with 2-oxoglutarate was purified 588-fold to homogeneity from Candida guilliermondii var. membranaefaciens, grown with 4-aminobutyrate as sole source of nitrogen. An apparent relative molecular mass of 107,000 was estimated by gel filtration. The enzyme was found to be a dimer made up of two subunits identical in molecular mass (Mr 55,000). The enzyme has a maximum activity in the pH range 7.8-8.0 and a temperature optimum of 45 degrees C. 2-Oxoglutarate protects the enzyme from heat inactivation better than pyridoxal 5'-phosphate. The absorption spectrum of the enzyme exhibits two maxima at 412 nm and 330 nm. The purified enzyme catalyzes the transamination of omega-amino acids; 4-aminobutyrate is the best amino donor and low activity is observed with beta-alanine. The Michaelis constants are 1.5 mM for 2-oxoglutarate and 2.3 mM for 4-aminobutyrate. Several amino acids, such as alpha,beta-alanine and 2-aminobutyrate, are inhibitors (Ki = 38.7 mM, Ki = 35.5 mM and Ki = 33.2 mM respectively). Propionic and butyric acids are also inhibitors (Ki = 3 mM and Ki = 2 mM).

Purification and characterization of amphiphilic trehalase from rabbit small intestine

Rabbit intestinal trehalase (alpha,alpha-trehalose glucohydrolase, EC 3.2.1.28) was solubilized with Triton X-100 and purified in the presence of EDTA. The purified enzyme was homogeneous on polyacrylamide gel electrophoresis in the presence of Triton X-100 or SDS. It showed amphiphilic properties on gel filtration. polyacrylamide gel electrophoresis, charge-shift electrophoresis and phenyl-Sepharose chromatography. Its molecular weight was estimated to be about 330 000 by gel filtration under nondenaturing conditions and in the presence of Triton X-100, the value being in satisfactory agreement with the sum of the weight of one Triton X-100 micelle and twice the molecular weight (105 000) of purified hydrophilic trehalase which had been deprived of the anchor segment. The two purified trehalases gave almost the same molecular weights (about 75 000) on SDS-polyacrylamide gel electrophoresis. These results suggest that intestinal trehalase consists of two subunits with a molecular weight of 75 000 and that its anchor segment is small (less than 5000). Triton X-100 extracts freshly prepared from intestinal microvilli essentially showed one form of trehalase, which behaved on phenyl-Sepharose and Con A-Sepharose chromatography in the same manner as purified amphiphilic trehalase.

Rat intestinal brush border membrane trehalase: some properties of the purified enzyme

Rat intestinal brush border trehalase (EC 3.2.1.28) solubilized by Triton X-100 or Emulphogen BC 720 has been purified almost to homogeneity in a five steps procedure including DEAE cellulose, Sephadex G-200, preparative flat bed electrofocusing and hydroxylapatite. The apparent molecular weight was estimated to be about 65,500 daltons by mannitol density gradient ultracentrifugation. The optimum pH of the enzyme was between 5.5 and 5.7 in phosphate, maleate or citrate buffers. The apparent Km for trehalose was found to be 10 mM in maleate buffer pH 6.0. The isoelectric point was 4.9. Tris, P-aminophenylglucoside, sucrose and maltose are fully competitive inhibitors with Kis of 2.2, 1.8, 7.7 and 170 mM, respectively. The inhibition by Phloridzin appeared to be of the mixed type with a Ki of 1.7 mM. Trehalase is heat stable up to 50 degrees C and the activation energy is 10.96 kcal/mol. Schiff's staining on polyacrylamide gel and interaction with Con-A-Sepharose indicate that rat trehalase is a glycoprotein.

Renal trehalase: two subsites at the substrate-binding site

Phlorizin, phloretin, Tris and beta-methylglucoside are competitive inhibitors, with respect to the substrate trehalose, of purified renal trehalase. Mercuric chloride is a noncompetitive inhibitor. The active site of trehalase was examined further by multi-inhibition kinetic studies involving combinations of inhibitors. Phlorizin vs. phloretin and phlorizin vs. Tris were mutually non-competitive. In contrast, phloretin vs. Tris was mutually competitive. These findings suggest that the binding site of phlorizin to the enzyme differed from that of phloretin or Tris, and that phloretin and Tris might bind at a common site. These findings suggest a model in which trehalase has two binding sites at the substrate-binding site, a phlorizin (glucosyl) and a phloretin (phenyl) binding site, analogous to the model proposed previously for the glucose carrier. In addition, mercuric chloride vs. beta-methylglucoside was mutually competitive, although mercuric chloride and beta-methylglucoside, respectively, were noncompetitive and competitive inhibitors with respect to the substrate. Thus, it is suggested that the substrate binding and the SH-inhibitor binding sites are located very close to each other.

Elevation of urinary trehalase in mercuric chloride-induced nephrotoxic rabbits: urinary trehalase as a specific indicator of renal brush border damage

The origin of urinary trehalase in mercuric chloride-induced nephrotoxic rabbits was demonstrated with biochemical and immunochemical techniques. Urinary trehalase was dramatically increased with HgCl2-induced nephrotoxicity. The nephrotoxic kidney showed an extreme decrease in specific fluorescence with fluorescein isothiocyanate (FITC)-conjugated antibody technique. Moreover, trehalase activity in the membrane fraction was remarkably decreased in the nephrotic kidney compared with the control. Judging from the results of immunodiffusion, urinary trehalase and renal trehalase exhibit the same antigenicity. From the data of a time course analysis of nephrotoxicity, the excretion of urinary trehalase was earlier than that of urinary sugar. Previous results show that renal trehalase is localized in the renal tubular brush borders. From these results, it is suggested that urinary trehalase is originated in the renal brush borders. In consideration of the results described in previous papers and in this paper, it is proposed that urinary trehalase is a good indicator of renal brush border damage.

Purification and properties of 2-aminoethylphosphonate:pyruvate aminotransferase from Pseudomonas aeruginosa

2-Aminoethylphosphonate aminotransferase has been purified to homogeneity with a yield of 15% from cell extracts of Pseudomonas aeruginosa. The molecular weight of the enzyme was estimated by gel filtration to be 65000 +/- 2000. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis yielded a molecular weight of 16500 +/- 1000, suggesting a tetrameric model for this protein. The absorption spectrum exhibits maxima at 280 nm, 335 nm and 415 nm which are characteristic of a pyridoxal-phosphate-dependent enzyme: 4 mol of pyridoxal 5'-phosphate/mol of enzyme have been found. This aminotransferase catalyzes the transfer of the amino group of 2-aminoethylphosphonate (ciliatine) to pyruvate to give 2-phosphonoacetaldehyde and alanine. A pH optimum between 8.5-9 and an activity increasing from 30 degrees C to 50 degrees C have been observed. The reaction follows Michaelis-Menten kinetics with Km values of 3.85 mM and 3.5 mM for ciliatine and pyruvate respectively. This enzyme shows a very high specificity since ciliatine and pyruvate are the only amino donor and acceptor respectively. Methyl, ethyl and propylphosphonic acids are better competitors towards ciliatine than their alpha-amino derivatives. 3-Aminopropylphosphonate, the higher homologue of ciliatine, is recognized neither as a substrate nor as an inhibitor. The enzyme activity is significantly affected by carbonyl reagents and by HgCl2. Transamination of 2-aminoethylphosphonate is the first step of a double-step pathway which leads to the cleavage of its C-P bond.

Effect of inorganic anions of the inhibition of trehalase activity by mercuric chloride

Monovalent inorganic anions showed an unexpected effect on the inhibition of trehalase (alpha, alpha-trehalose glucohydrolase, EC 3.2.1.28) by SH inhibitors. This phenomeon (deinhibition) was caused by monovalent anions, Cl-, Br-, I- and SCN- . F- and ClO4- showed partial deinhibition. Deinhibition was not caused by NO2- and SO4-. The effectiveness of the "active anions' in causing deinhibition was highly dependent on the anion size. Trehalase in the presence of mercuric chloride was "activated' by Cl-, and the activation was saturable. From the results of Dixon plots for trehalase at different concentrations of the "activator' (deinhibitor) and a constant concentration of the substrate, it can be seen that the activator and the inhibitor competed with each other. Thus, it is suggested that the activator and the inhibitor share a common binding site or bind very near each other. The Ki value for mercuric chloride was increased with increasing concentration of NaCl. Therefore, it might be essential to remove the "active anions' in order to determine the inhibitory effect and the Ki value of trehalase for SH inhibitors.

Sugar hydrolases and their arrangement on the rat intestinal microvillus membrane

The arrangement of the sugar hydrolases, sucrase-isomaltase, maltase, and lactase on the microvillus membrane of rat intestine was investigated by immunological technique. The enzymes were purified essentially free of each other to near homogeneity and antisera of high specificity were obtained against each. Microvillus membranes were prepared routinely in high purity from rat intestine and contained an average 61% protein, 20% lipid, and 19% carbohydrate, with the sugar hydrolases comprising an estimated 20--25% of the membrane protein. The immunoreactivity of membrane-bound sucrase-isomaltase, maltase, and lactase was investigated with antisera demostrating specific reactivity to each, when tested in the presence of other membrane extractives. The membrane-bound enzymes were found in each case to combine with antibody in amounts equivalent to that required to effect precipitation of comparable units of the free enzymes from solution. Preloading membrane vesicles with antibodies to any two of the enzymes did not affect either the immunoreactivity or extractability (by papain or Triton X-100) of the third. The antibody-binding studies indicated an arrangement of these enzymes independent of each other on the membrane surface, in a manner allowing each to maintain a high degree of molecular freedom.

Purification and properties of trehalase from the thermophilic fungus Humicola lanuginosa

Trehalase (alpha,alpha-Trehalose glucohydrolase, EC 3.2.1.28) was partially solubilized from the thermophilic fungus Humicola lanuginosa RM-B, and purified 184-fold. The purified enzyme was optimally active at 50 degrees C in acetate buffer at pH 5.5. It was highly specific for alpha,alpha-trehalose and had an apparent Km = 0.4 mM at 50 degrees C. None of the other disaccharides tested either inhibited or activated the enzyme. The molecular weight of the enzyme was around 170 000. Trehalase from mycelium grown at 40 and 50 degrees C had similar properties. The purified enzyme, in contrast to that in the crude-cell free extract, was less stable. At low concentration, purified trehalase was afforded protection against heat-inactivation by "protection against heat-inactivation by "protective factor(s)" present in mycelial extracts. The "protective factor(s)" was sensitive to proteolytic digestion. It was not diffusible and was stable to boiling for at least 30 min. Bovine serum albumin and casein also protected the enzyme from heat-inactivation.

Properties of taurine: alpha-ketoglutarate aminotransferase of Achromobacter superficialis. Inactivation and reactivation of enzyme

The activity of taurine: alpha-ketoglutarate aminotransferase (taurine: 2-oxoglutarate aminotransferase, EC 2.6.1.55) from Achromobacter superficialis is significantly diminished by treatment of the enzyme with (NH4)2SO4 in the course of purification, and recovered by incubation with pyridoxal phosphate at high temperatures such as 60 degrees C. The inactive form of enzyme absorbing at 280 and 345 nm contains 3 mol of pyridoxal phosphate per mol. The activated enzyme contains additional 1 mol of pyridoxal phosphate with a maximum at 430 nm. This peak is shifted to about 400 nm as a shoulder by dialysis of the enzyme, but the activity is not influenced. The inactive form is regarded as a partially resolved form, i.e. a semiapoenzyme. The enzyme catalyzes transamination of various omega-amino aicds with alpha-ketoglutarate, which is the exclusive amino acceptor. Hypotaurine, DL-beta-aminoisobutyrate, beta-alanine and taurine are the preferred amino donors. The apparent Michaelis constants are as follows; taurine 12 mM, hypotaurine 16 mM, DL-beta-aminoisobutyrate 11 mM, beta-alanine 17 mM, alpha ketoglutarate 11 mM and pyridoxal phosphate 5 micron.

Isolation and properties of fecal proteins and fecal alkaline phosphatase from germfree and conventional rats

Fecal proteins from germfree and conventional rats were isolated. The proteins from the two kinds of feces differed in molecular weight, judging from Sephadex gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The conventional feces contained a greater amount of high-molecular-weight and a lesser amount of low-molecular-weight proteins than did the germfree feces. The fecal proteins of both kinds contained carbohydrates. Both feces contained considerable enzyme activity. The germfree feces contained extremely high activity in alkaline phosphatase and leucine aminopeptidase. Both feces showed the same level of trehalase activity. The conventional feces contained higher levels of activity of protease and acid phosphatase than did the germfree feces. Lactase activity was observed only in the conventional feces. The fecal alkaline phosphatase resembled the intestinal enzyme in response to L-phenylalanine inhibition and urea denaturation. From these results it was inferred that the germfree feces contained some of the intestinal proteins and that the conventional feces contained bacterial proteins in addition to intestinal proteins.