Intestinal lactase (beta-galactosidase) and other glycosidase activities in suckling and adult tammar wallabies (Macropus eugenii)

The activities of various glycosidases in homogenates of the small intestinal mucosa of two adult and 18 suckling tammar wallabies (M. eugenii) aged from 6 to 50 weeks were investigated. Lactase (beta-D-galactosidase), beta-N-acetylglucosaminidase, alpha-L-fucosidase and neuraminidase activities were high during the first 34 weeks post partum and then declined to very low levels. Maltase, isomaltase, sucrase and trehalase activities were very low or absent during the first 34 weeks, and then increased. The lactase activity was unusual in being greater in the distal than the middle or proximal thirds of the intestine, and in its low pH optimum (pH 4.6), inhibition by p-chloromercuribenzene sulfonate but not by Tris, and lack of cellobiase activity. These properties are those of a lysosomal acid beta-galactosidase rather than of a brush border neutral lactase. The maltase activity had the characteristics of a lysosomal acid alpha-glucosidase early in lactation and of a brush border neutral maltase in adult animals. The significance of these findings is discussed in relation to changes in dietary carbohydrates during weaning and to the mode of digestion of milk carbohydrates by the pouch young.     

Human small-intestinal β-galactosidases. Separation and characterization of one lactase and one hetero β-galactosidase

1. Two beta-galactosidases from human small-intestinal mucosa were separated by gel-filtration chromatography and the properties of the two enzymes were studied. Lactose and four hetero beta-galactosides were used as substrates. 2. One of the enzymes was particle-bound and could be partially solubilized with papain. Of the substrates hydrolysed by this enzyme, lactose was hydrolysed most rapidly. This enzyme is thus essentially a disaccharidase and is named lactase. It is presumably identical with the ;lactase 1' described earlier. 3. The other enzyme was mainly soluble and hydrolysed all artificial substrates used, whereas no lactase activity could be detected. This enzyme has therefore been designated hetero beta-galactosidase. 4. p-Chloromercuribenzoate (0.1mm) inhibited the hetero beta-galactosidase completely but did not influence the activity of the lactase. Tris was a competitive inhibitor of both enzymes. 5. The residual lactase activity in the mucosa of lactose-intolerant patients may be exerted by a small amount of remaining lactase as such, or possibly by a third enzyme with a more acid pH optimum.     

Intestinal lactase and other disaccharidase activities of a suckling crabeater seal (Lobodon carcinophagus)

1. The intestinal disaccharidase activities of a suckling crabeater seal were investigated. 2. Lactase, maltase, isomaltase and cellobiase activities were readily detected but trehalase and sucrase activities were absent. 3. The intestinal homogenates were separated into a soluble (S2) fraction and a particulate brush border (P2) fraction. The lactase activities of the two fractions had different properties corresponding to those of an acid and a neutral beta-galactosidase respectively. Approximately two-thirds of the total lactase activity measured at pH 6.0 was due to the acid beta-galactosidase. 4. The isomaltase and cellobiase activities were found almost exclusively in the particulate fractions but about one third of the maltase activity was in the S2 fraction. This soluble maltase activity appeared to be due to an acid maltase.     

Indigogenic methods for glycosidases

Summary 4-Cl-5-Br-3-indolyl--D-fucoside (IbF) was tested in histochemical and bio-chemical experiments. Sections from differently treated parts of the small intestine of suckling and adult rats, of jejunum of adult hamsters, guinea pigs, cooks, monkeys, of human jejunal biopsies, of kidney of suckling and adult rats, adult monkeys, guinea pigs and hamsters, and of some other rat organs were used in histochemical experiments. Neutral and acid -D-galactosidases prepared from homogenates of the small intestine of suckling rats by chromatography on Sephadex G 200 were used in biochemical experiments.The recommended medium for histochemical studies consists of 0.1 M citrate phosphate buffer pH 6 (brush border enzyme) and pH 4 (lysosomal enzyme), 3.6·10^–4M IbF and 3.1·10^–3 M potassium ferri- and ferrocyanide.IbF is split quite efficiently by the brush border -D-galactosidase (=lactase) and the recommended histochemical method with IbF at pH 6 is the method of choice in studies concerned with the localization of intestinal lactase. In unfixed cold microtome sections the brush border activity can be easily detected within 15–240 minutes, depending on the lactase activity of the studied sample. In this study this activity was shown to be present in the brush border of enterocytes in the upper part of crypts reaching its maximum in differentiated enterocytes covering the sides and tops of villi in the small intestine of suckling (the highest activity) and adult rats (3–4x lower activity according to the time of appearance of the staining), and of human, monkey and hamster jejunum. In the cock jejunum traces of brush border staining were seen only after 24 hours of incubation. In enterocytes of patients with celiac sprue the brush border activity was very much reduced in dependence on the stage of the disease. Brush border staining along with a diffuse cytoplasmic reaction was found in the proximal convoluted tubules of the monkey kidney. The question of localization of enzyme activity splitting IbF in the monkey kidney deserves further investigation.IbF is also split by isolated intestinal acid -D-galactosidase and histochemically a positive reaction was found in lysosomes of many cells displaying a high activity of -D-galactosidase when IbF was used in the recommended medium of pH 4. The use of aldehyde fixation (glutaraldehyde is to be preferred) is a prerequisite for the assessment of this lysosomal localization. The lysosomal activity splitting IbF is not firmly bound structurally and escapes from cold microtome sections prepared from unfixed tissue samples into the incubation solution.The recommended method is also very suitable for processing zymograms and immunoprecipitation lines of lactase with antisera obtained by Ouchterlony's technic and by immunoelectrophoresis.     

Human small-intestinal β-galactosidases. Separation and characterization of three forms of an acid β-galactosidase

1. An acid beta-galactosidase, optimum pH4.0-4.5, in the human small-intestinal mucosa was separated and characterized. 2. Autolysis of mucosal homogenates at acid pH inactivated the lactase and hetero beta-galactosidase; the total activity of the acid beta-galactosidase was only slightly depleted, but a greater proportion of the enzyme was solubilized by this treatment. 3. Separation on a Sephadex G-200 column revealed that the acid beta-galactosidase could occur in at least three different forms, probably representing monomer, dimer and octamer or polymer of the enzyme. 4. The properties of the different forms of the acid beta-galactosidase were studied with regard to pH optimum, K(m), rate of hydrolysis of different substrates, and sensitivity to p-chloromercuribenzoate and tris as inhibitors. All these properties were the same for the different forms of the enzyme. 5. The acid beta-galactosidase hydrolyses lactose as well as hetero beta-galactosides and contributes to the lactase activity of intestinal biopsies also when measured at pH 6. This enzyme may therefore be responsible for a considerable part of the residual lactase activity found in lactose-intolerant patients.     

Rat small-intestinal β-galactosidases. Kinetic studies with three separated fractions

1. Three fractions of beta-galactosidase activity from the rat small-intestinal mucosa were separated chromatographically. Two of these fractions had an acid pH optimum at 3-4, and the third one had a more neutral pH optimum at 5.7. 2. The two ;acid' beta-galactosidase fractions had considerably lower K(m) values for hetero beta-galactosides than for lactose. The V(max.) values were similar for all the substrates used (lactose, phenyl beta-galactoside, o-nitrophenyl beta-galactoside, p-nitrophenyl beta-galactoside and 6-bromo-2-naphthyl beta-galactoside). No difference could be detected between the two ;acid' fractions with respect to their enzymic properties (pH optimum, K(m) for the different substrates, K(i) for lactose as an inhibitor of the hydrolysis of hetero beta-galactosides, K(i) for phenyl beta-galactoside as an inhibitor of the hydrolysis of lactose, and relative V(max.) for the hydrolysis of different substrates). These two fractions probably represent different forms of the same enzyme. 3. The ;neutral' fraction had similar K(m) values for all the substrates hydrolysed, but with lactose as substrate the V(max.) was much higher than with the hetero beta-galactosides. This fraction did not split phenyl beta-galactoside or 6-bromo-2-naphthyl beta-galactoside at a measurable rate. 4. Lactose was a competitive inhibitor of the hetero beta-galactosidase activities of all the three fractions, and K(i) for lactose as an inhibitor in each case was the same as K(m) for the lactase activity. Phenyl beta-galactoside was a competitive inhibitor of the lactase activity of all the three fractions. These facts strongly indicate that in all the three fractions lactose is hydrolysed by the same active sites as the hetero beta-galactosides. 5. Human serum albumin stabilized the separated enzymes against inactivation by freezing and thawing.     

Absence of beta-galactosidase (lactase) activity from intestinal brush borders of suckling macropods: implications for mechanism of lactose absorption

1. Neutral beta-galactosidase (lactase) activity was absent from crude brush borders of small intestines of three species of suckling macropods (kangaroos and wallabies), even though the intestinal mucosal homogenates had high beta-galactosidase activities. 2. These activities were entirely due to an intracellular acid beta-galactosidase, probably located in lysosomes. 3. The results suggest that the absorptive-digestive mechanism for lactose in macropods is fundamentally different from that in eutherian mammals.     

Carbohydrase activities in the bovine digestive tract

1. The carbohydrase activities of homogenates of mucosa from the abomasum, small intestine, caecum and colon, and of the pancreas of cattle were studied. 2. The disaccharidase activities were located mainly in the small intestine and showed a non-uniform pattern of distribution along the small intestine; trehalase activity was highest in the proximal part, lactase and cellobiase activities were highest in the proximal and middle parts and maltase activity was highest in the distal part. 3. The intestinal lactase and cellobiase activities were highest in the young calf and decreased with age, whereas the intestinal maltase and trehalase activities, which were very low compared with the lactase activity, did not change with age. 4. No intestinal sucrase or palatinase activity was detected in the calf or in the adult cow. 5. Homogenates of intestinal mucosa also exhibited amylase and dextranase activity. 6. Homogenates of the pancreas possessed a strong amylase activity and a weak maltase activity. The maltase activity did not change with age, whereas the amylase activity increased with age. 7. No marked differences were observed between the carbohydrase activities of calves fed solely on milk and those of calves given a concentrate-hay diet from 6 weeks of age.     

Hormone induced changes in lactase glycosylation in developing rat intestine

Lactase exists in both soluble and membrane-bound forms in suckling rat intestine. The distribution of lactase and its glycosylated isoforms in response to thyroxine or cortisone administration has been studied in suckling rats. 75% of lactase activity was detected, associated with brush borders, compared to 24% in the soluble fraction of 8-day-old rats. Thyroxine treatment enhanced soluble lactase activity to 34%, whereas particulate fraction was reduced to 67% compared to controls. Cortisone administration reduced soluble lactase activity from 24% in controls to 12% with a concomitant increase in membrane-bound activity to 89%. Western blot analysis revealed lactase signal, corresponding to 220 kDa in both the soluble and membrane fractions, which corroborated the enzyme activity data. The elution pattern of papain solubilized lactase from agarose-Wheat Germ agglutinin, or Concanavalin A or Jacalin agglutinin columns was different in the suckling and adult rat intestines. Also the elution profile of lactase activity from agarose-lectin columns was modulated in cortisone, thyroxine, and insulin injected pups, which suggests differences in glycosylated isoforms of lactase under these conditions. These findings suggest the role of these hormones in inducing changes in lactase glycosylation during postnatal development of intestine, which may contribute to adult-type hypolactasia in rats.     

Short-term effects of spermine ingestion on the small intestine: a comparison of suckling and weaned rats

We have previously shown that spermine, shortly after its ingestion, can induce the alteration of the morphology of the small intestine of suckling rats. It was proposed that this alteration is due to polyamine accumulation inside the epithelial cells. This could also be related to the fact that the intestine of the suckling rat is in an immature state. To shed light on this issue, disaccharidase and alkaline phosphatase activity assays, protein, DNA and RNA content measurements and polyamine concentration analysis were performed on the small intestine of suckling and weaned Wistar rats treated with spermine. Spermine did not induce the same intestinal alterations in weaned rats compared to suckling animals. Indeed, in sucklings, spermine administration induced a decrease of the protein, DNA, putrescine and spermidine intestinal content, suggesting a cell loss. The cell loss impaired the activity of intestinal enzymes: lactase, maltase and alkaline phosphatase. In weaned rats, the same treatment did not alter these parameters. Exogenous spermine by itself is not sufficient to induce the alterations described here and previously. The maturity degree of the small intestine could be the basis of this process.     

Activities of enzymes of ketone-body utilization in brain and other tissues of suckling rats

1. The activities of 3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase in rat brain at birth were found to be about two-thirds of those of adult rat brain, expressed per g wet wt. The activities rose throughout the suckling period and at the time of weaning reached values about three times higher than those for adult brain. Later they gradually declined. 2. At birth the activity of acetoacetyl-CoA thiolase in rat brain was about 60% higher than in the adult. During the suckling period there was no significant change in activity. 3. In rat kidney the activities of the three enzymes at birth were less than one-third of those at maturity. They gradually rose and after 5 weeks approached the adult value. Similar results were obtained with rat heart. 4. The activity of glutamate dehydrogenase (a mitochondrial enzyme like 3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase) also rose in brain and kidney during the suckling period, but at no stage did it exceed the adult value. 5. Throughout the suckling period the total ketone-body concentration in the blood was about six times higher than in adult fed rats, and the concentration of free fatty acids in the blood was three to four times higher. 6. It is concluded that the rate of ketone-body utilization in brains of suckling rats is determined by both the greater amounts of the key enzymes in the tissue and the high concentrations of ketone bodies in the blood. In addition, the low activities of the relevant enzymes in kidney and heart of suckling rats may make available more ketone bodies for the brain.     

Insulin accelerates the development of intestinal brush border hydrolytic activities of suckling mice

The influence of insulin on the postnatal development of intestinal brush border membrane disaccharidase (sucrase, maltase, trehalase, lactase) and peptidase (leucylnaphthylamidase, γ-glutamyltranspeptidase) activities has been studied in mice. At 8 days of age, the animals received either 5, 10, or 12.5 mU insulin/g body wt/day during 3 days. A premature appearance of sucrase activity was noted, the level of sucrase activity being dependent of the amount of insulin injected. Maltase and lactase activities were both increased while trehalase activity was affected only by the highest dose of insulin. The behavior of the two peptidases was quite different as γ-glutamyltranspeptidase was prematurely increased and leucylnaphthylamidase was unaffected by insulin. The hormonal effect is exerted along the entire small intestine. The time course of the responses of the disaccharidases in relationship to cellular migration along the crypt-villus axis has also been studied. By 24 hr after administration of a single injection of 12.5 mU insulin/g body wt, sucrase activity was already present and an increased maltase and trehalase activities were observed. During the subsequent 72 hr no further increase of enzymatic activity was noted even though the epithelial cells are moving up on the villi at a faster rate than in controls, thus indicating that there is no relationship between the enzymatic responses and the cellular migration. The present data show that a premature increase of the circulating level of insulin influences the development of intestinal mucosa in suckling mouse.     

Monoacylglycerol acyltransferase. Evidence that the activities from rat intestine and suckling liver are tissue-specific isoenzymes

The monoglycerol acyltransferase (EC 2.3.1.22) (recommended name acylglycerol palmitoltransferase) activities from rat intestinal mucosa and suckling liver microsomes were compared in order to determine why substrate specificities differed in the two tissues. Suckling liver monoacylglycerol acyltransferase activity was highly specific for sn-2-mono-C18:1 glycerol and acylated rac-1-mono-C18:1 glycerol and 1- and 2-mono-C18:1 glycerol ethers poorly. In contrast, the substrate specificity of intestinal monoacylglycerol acyltransferase activity was broad. 1-Acyl- and 1- and 2-alkylglycerols were acylated at rates that were 45-78% of the rate observed with the preferred substrate sn-2-mono-C18:1 glycerol. Partial heat inactivation did not alter these relative specific activities, making it unlikely that intestinal microsomes contained a second acyltransferase capable of acylating the alternate substrates. The hypothesis that intestine and liver contain non-identical monoacylglycerol acyltransferase activities was further tested. Intestinal mucosa monoacylglycerol acyltransferase was much more thermolabile than the liver activity. Incubation with 50 microM diethylpyrocarbonate inactivated liver monoacylglycerol acyltransferase activity 84% but had little effect on the intestinal activity. Hydroxylamine completely reversed diethylpyrocarbonate inactivation, suggesting that critical histidine residues were more accessible in liver monoacylglycerol acyltransferase. 2,4,6-Trinitrobenzene sulfonic acid inactivated hepatic monoacylglycerol acyltransferase more than the intestinal activity, suggesting that critical lysine residues were more accessible. The intestinal and liver activities were also differently affected by acetone, detergents, MgCl2, phospholipids, and bovine serum albumin. Taken as a whole, the data strongly suggest that rat intestinal mucosa and suckling liver contain tissue-specific monoacylglycerol acyltransferase isoenzymes.     

Influence of Microcystin-LR on the activity of membrane enzymes in rat intestinal mucosa

The objective of the present study was to evaluate the effects of microcystin-LR (MCLR) on the activity of membrane enzymes from intestinal mucosa. In addition, serum chemistry and peroxidative status of both serum and intestinal homogenate were evaluated after treatment with MCLR. Wistar rats were treated with intraperitoneal injection of either 100 microg pure MCLR/Kg body weight or saline solution. A significant increase in liver weight and altered serum enzyme activities were found in MCLR-treated rats, indicating damage to the liver in these rats, as previously suggested. A higher specific activity of sucrase (1.5-fold) was observed after the administration of MCLR, whereas other intestinal apical membrane enzymes, such as lactase, maltase and alkaline phosphatase were not modified by the treatment. The specific activities of acid phosphatase and succinate dehydrogenase, markers for lysosomal and mitochondrial membranes, respectively, were also increased (32% and 60%, respectively) in treated rats. The analysis of lipid peroxidation showed that the peroxidative status was increased in both serum and intestinal mucosa from MCLR-treated rats, reflecting an excess production of oxygen free radicals induced by this cyanobacterial toxin. In conclusion, this study shows that acute exposure to MCLR affects the intestinal physiology by modifying the intestinal peroxidation status as well as the activity of membrane enzymes.     

Acid hydrolases in the suckling rat small intestine. II. On the importance of alkaline phosphatase inhibition in the histochemical localization of acid phosphatase activity.

Phosphatase activities against beta-glycerophosphate, I-naphthyl phosphate and naphthol AS-TR phosphate were investigated, at acid and aldaline pH levels, using unfixed and fixed cryostat sections of suckling rat jejunum. The use of 10 mm EDTA and 10 mm NaF as inhibitors indicated that alkaline phosphate is predominantly located in the microvillous region of the adsorptive cells, while acid phosphatase is located in small particles distributed between the brush borders and the nuclei of these cells. Alkaline phosphatase activity was found to interfere with the localization of acid phosphatase unless EDTA was included in the incubation medium. A modified Gomori medium, containing 10 mm EDTA and additional lead nitrate, is described. Latency experiemtns using this medium, with unfixed sections, indicated the lysosomal nature of particulate acid phosphatase. The discussion stresses the importance of including an aldaline phosphatase inhibitor in incubation media designed to localize extralysosomal acid phosphatase activity.