The diversity of alkaline phosphatase from rat intestine. Isolation and purification of the enzyme (s)

Effect of calcium on rat intestinal alkaline phosphatase activity and molecular aggregation

Two fractions of rat intestinal alkaline phosphatase (IAP) were detected by Western blot: 168 +/- 6 and 475 +/- 45 kDa. The low molecular weight fraction constitutes 43% of the isolated proteins exhibiting 82% of the enzymatic activity, and a heavier fraction constitutes 57% of the isolated proteins and has 18% of the enzymatic activity. Calcium produced an increase of the 475-kDa form to the detriment of the 168-kDa form. This work also describes the kinetic and structural changes of IAP as a function of calcium concentration. With [Ca2+] < 10 mmole/L, the Ca(2+)-IAP interaction fitted a binding model with 7.8 +/- 4.4 moles of Ca2+ /mole of protein, affinity constant = 19.1 +/- 8.4 L/mmole, and enzymatic activity increased as a linear function of [Ca2+] (r = 0.946 p < 0.01). On the other hand, with [Ca2+] > 10 mmole/L the data did not fit this model and, the enzymatic activity decreased as a function of [Ca2+] (r = - 0.703 p < 0.05).

Distribution and properties of rat intestinal alkaline phosphatase isoenzymes

The ALP activities and properties of rat intestine cut into 20 segments were examined, and we were able to demonstrate that the ALP activity of upper intestine is high compared to that of lower intestine. This result coincided with those of other reports. However, we newly clarified that there is an ALP isoenzyme found in the lower intestine which can be inhibited by L-homoarginine. The molecular weight of the ALP isoenzyme was 136 kDa. In addition, it was clarified that there are several isoenzymes from upper to lower intestine. This study demonstrates that there exist isoenzymes, which are inhibited by L-HArg, in the intestine which are similar to the isoenzymes in the liver, bone and kidney.

A quantitative histochemical study of alkaline phosphatase activity in isolated rat duodenal epithelial cells

A simple separation method enabling the quantification of alkaline phosphatase activity in unfixed, isolated, individual, duodenal epithelial cells has been presented. The activity of intestinal brush border-bound alkaline phosphatase has been demonstrated using naphthol AS-BI phosphate as a substrate and hexazotized New Fuchsin as a simultaneous coupling agent. The amount of final reaction product, as measured cytophotometrically, increases linearly with incubation time (up to 10 min) and with substrate concentration (up to 0.4 mM). Maximum enzyme activity was obtained at pH 8.9. Variation of the substrate concentration revealed the kinetic parameters for naphthol AS-BI phosphate as Km = 0.17 i 0.015 and Vmax = 13.9 +/- 1.38. The specificity of the enzyme reaction was confirmed by the complete inhibition of the enzyme activity in the presence of L-cysteine (10 mm) and 80% inhibition with L-phenylalanine (30 mM). Comparison of alkaline phosphatase activity in 8-microm cryostat sections (beginning at the tip and proceeding to the cryptal part) along the villus axis, with the activity of individual cells obtained by successive separation, revealed similar values of the percentage quotient derived from the entire activities in these two different methods. This suggests that the presented separation procedure gives rise to isolation of the respective cells from the corresponding areas of the villus. Finally, the isolated cells can be used as a valuable tool for the quantitative analysis of alkaline phosphatase activity along the length of the villus.

Role of sodium azide in reducing nonspecific color development in enzyme immunoassays

Improved enzyme immunoassay (EIA) procedures achieved by incorporating sodium azide during predilution of serum samples in a solid-phase EIA for the detection of anti-Toxoplasma antibody in swine using a peroxidase conjugate and in all washes of a bovine brucellosis rapid card test EIA using alkaline phosphatase conjugate are reported. Without this modification, substantial background interference was encountered that showed direct correlation with the degree of hemolysis of the serum samples. Anti-Toxoplasma gondii antibody-negative samples, separated by subjective groupings based on degree of hemolysis, into "clear", "slight", and "gross/total" samples, had a mean +/- standard deviation of 0.150 +/- 0.072, 0.187 +/- 0.105, and 0.232 +/- 0.108, respectively. The incorporation of sodium azide during the initial step of serum dilution dramatically eliminated the background, giving a mean +/- standard deviation of 0.079 +/- 0.029, 0.076 +/- 0.022, and 0.081 +/- 0.029, respectively. The level of endogenous peroxidase activity, a possible factor for this nonspecific interference, was considerably elevated in some of the swine sera. The clear, slight, and gross/total categories had relative levels of 1%, 2%, and 51% peroxidase activity compared to the conjugate peroxidase activity of 100%. Whereas sodium azide could be used only in sample predilution in the swine toxoplasmosis peroxidase-conjugate test, in the bovine brucellosis alkaline phosphatase-conjugate card test it could be used in all wash cycles. Many brucellosis card test results were visually uninterpretable because of significant background color when the manufacturer's wash reagent was used. The substitution of a wash reagent containing sodium azide eliminated background color, giving a visually unambiguous test.

Characterization of microvillar membrane proteins of dog small intestine by two-dimensional electrophoresis

A method for analysing microgram amounts of microvillar membranes by two-dimensional electrophoresis (protein mapping) is described, and has been used to characterize the microvillar proteins of the small intestine of German shepherd, corgi, and beagle dogs. Detergent-solubilized microvillar membranes were radiolabelled with 14C and separated by isoelectric focussing followed by SDS-PAGE. Proteins were detected fluorographically and glycoproteins by lectin-affinity staining. The microvillar hydrolases alkaline phosphatase and dipeptidyl aminopeptidase IV were identified by active-site labelling and aminopeptidase N by immunoprecipitation. Changes following pancreatic duct diversion were consistent with accumulation of pro-sucrase-isomaltase and diminished expression of the sucrase and isomaltase subunits. Cytoskeletal proteins were concentrated in the core fraction remaining after extraction of microvillar membranes with Triton X-100. There were no consistent differences between dogs of different breed, and the canine protein maps were similar to the human.

Isolation of a mRNA that encodes a putative intestinal alkaline phosphatase regulated by 1,25-dihydroxyvitamin D-3

Using differential hybridization techniques to screen a rat intestinal cDNA library we isolated a cDNA whose predicted amino acid sequence exhibits a high degree of homology to the alkaline phosphatases. The predicted cDNA sequence has 79% identity at the amino acid level to the rat intestinal alkaline phosphatase, and shows approx. 70% homology to other human and rat alkaline phosphatases. The corresponding mRNA is markedly increased by 6 h after a single dose of 1,25-dihydroxyvitamin D-3. The mRNA is also increased by 24-homologated analogs of 1,25-dihydroxyvitamin D-3 that do not increase calcium transport.

Purification and characterization of phytase from rat intestinal mucosa

Phytase (myo-inositol hexakisphosphate phosphohydrolase; EC 3.1.3.8 or 3.1.3.26) was purified from rat intestinal mucosa. The purified enzyme preparation exhibited two protein bands on SDS-polyacrylamide gel electrophoresis with estimated molecular masses of 70 kDa and 90 kDa. Rabbit antisera prepared against the 90K subunit cross-reacted with the 70K subunit on immunoblotting. The peptide maps of the 70K and 90K subunits were similar, and the N-terminal amino acid sequences of the two subunit proteins were almost identical. Treatments to remove sugar moieties from the proteins showed that the two subunit proteins had different oligosaccharide chains, although the difference in their molecular masses was not due to the difference in their oligosaccharide compositions. The purified enzyme also showed activity of alkaline phosphatase (orthophosphoric monoester phosphohydrolase; EC 3.1.3.1), but the properties of the two enzyme activities were different; the optimum pH for phytase activity was 7.5, while that for alkaline phosphatase was 10.4. Phytase activity did not necessarily require divalent cations, while Mg2+ was essential for alkaline phosphatase activity. Phenylalanine, a specific inhibitor of intestine-type alkaline phosphatase had no effect on the phytase activity.

Effect of some alkaline phosphatase inhibitors on intestinal calcium transfer

1. There is a good correlation between the capacity of sugars to stimulate calcium transfer and their capacity to be phosphorylated by the intestinal alkaline phosphate with a part of the phosphate liberated from an ester phosphate. 2. On the sugar dependent and sugar independent calcium transfer, inhibitors of this enzyme act differently. 3. Phosphate, a competitive inhibitor suppresses both transfers. 4. Only the dependent sugar transfer was suppressed with phloridzin acting competitively at the sugar site, or with EDTA which could react close to the active site. 5. L-phenylalanine and phenobarbital, not competitive inhibitors does not act on either type of calcium transfer, the sugar dependent or the sugar independent.

The effect of chronic parenteral administration of cadmium on isoenzyme levels of alkaline phosphate in intestinal mucosa

Chronic administration of cadmium chloride to rats (13.3 mumol/kg body wt per dose subcutaneously) produced a decrease in the activity of alkaline phosphatase in the intestinal mucosa to less than half that in control rats by the time cumulative doses of between 30 and 48 mumol had been administered. The reduced level of activity remained approximately steady following further dosing. Three isoenzymes of intestinal alkaline phosphatase were separated electrophoretically. Chronic cadmium treatment markedly decreased the proportion of the 2 isoenzymes with lower electrophoretic mobility. Some analogies are drawn between the effect of cadmium administration, and magnesium deficiency on changes in intestinal alkaline phosphatase.

Homodimer and heterodimer forms of adult rat intestinal alkaline phosphatase

Three forms of alkaline phosphatase have been isolated from different sections of the small intestine: F3 180 kDa from the duodenum; F2 150 kDa principally jejunal; F1 120 kDa the only ileal form. Their catalytic properties have been compared as well as the electrophoretic properties the dimer and monomer of their phosphorylated intermediates. Pi was a competitive inhibitor of F1 and F3, whereas glycerophosphate was competitive inhibitor only of F3. Pi was a non competitive inhibitor of F2 and of a mixture F1 plus F3. Heating the phosphorylated enzyme preparations led to their dissociation into the phosphorylated monomers: F1 and F3 appear to be homodimers 65 kDa and 90 kDa peptides respectively whilst F2 seems to be a dimer formed from one of each monomer. F1 was phosphorylated faster but less intensively than F3. F2 was strongly phosphorylated over a long time-course and its 65 kDa monomer fraction was phosphorylated more strongly for longer than that from F1.

Alkaline phosphatase isozymes in large intestines and large intestinal tumors of Fischer 344 rats

Eight electrophoretic forms of alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) were detected in butanol extracts of Fischer 344 rat large intestines. Seven of these isozymes have higher mobility than the small intestinal form(s) in non-denaturing polyacrylamide gel electrophoresis. These more mobile forms may be derived during extraction from more slowly migrating forms that are analogous to those forms found in the small intestine. Monoclonal antibody with specificity for a rat small intestinal isozyme cross-reacts with four of the large intestinal isozymes. This antibody does not cross-react with alkaline phosphatases from human or hog small intestine. Gel exclusion chromatography molecular weight estimates of rat intestinal forms range from 1.1 X 10(5) to 2.5 X 10(5). Alkaline phosphatase from two colon tumors obtained from azoxymethane treated rats appeared to be similar to an isozyme found in some normal rats, on the basis of electrophoretic mobility and cross-reactivity with the monoclonal antibody.

Heterogeneity of rat hepatocytes in transport and hepatic binding of asialoalkaline phosphatase studied after induction of selective acinar damage by N-hydroxy-2-acetylaminofluorene and carbon tetrachloride

In order to investigate rat hepatocyte heterogeneity in asialoglycoprotein transport, rats were pretreated with N-hydroxy-2-acetylaminofluorene (N-OH-AAF, 90 mumol/kg, i.v.) to damage zone 1 hepatocytes, or with carbon tetrachloride (CCl4, 2.1 mmole/kg, p.o.) to damage zone 3 hepatocytes. Twenty-four hours after pretreatment, the asialoglycoprotein dog intestinal alkaline phosphatase (As-ALPase) was injected and plasma disappearance and biliary excretion were measured. In addition, the acinar distribution of the hepatic binding of As-ALPase 10 min after injection in vivo, or after incubation of fixed liver sections with As-ALPase in vitro, was determined by enzyme histochemistry. In control rats, a rapid biexponential plasma disappearance was observed and 6.4 +/- 1.5% of the dose was excreted into bile after 60 min. Hepatocyte binding occurred predominantly in zone 3, both after administration in vivo and after incubation with liver sections in vitro. In rats with zone 1 liver damage, both the half-lives of the first and of the second phase were strongly increased, but biliary excretion did not change significantly. Both in vivo and in vitro the relatively weak binding of As-ALPase in zone 1 of the liver was abolished, whereas binding to zone 3 cells was normal or only slightly decreased. After CCl4-pretreatment histochemically detectable binding to zone 3 cells was completely abolished, leaving only the relatively weak binding in zone 1. Unexpectedly, a normal plasma disappearance and biliary excretion rate were found in these rats. The discrepancy between the pharmacokinetic results, which point to a predominant involvement of zone 1 cells in As-ALPase transport, and the enzyme histochemical studies, which show preferential binding of As-ALPase in zone 3, is discussed.

The effect of zinc deficiency on alkaline phosphatase (EC 3.1.3.1) and its isoenzymes

1. Zinc deficiency in young rats reduced both the total alkaline phosphatase (EC 3.1.3.1) activity and Zn concentration in serum, kidney, small intestine and femur. 2. Addition of 0.01 mM-exogenous Zn had no greater activating effect with extracts of kidney, small intestine and femur from Zn-deficient than control rats, indicating that the main effect of the deficiency was on the amount of enzyme present rather than the efficiency of its operation. Exogenous Zn increased the activity of enzyme in serum Zn-deficient rats, but it was still lower than in the serum of control animals. 3. Electrophoresis on polyacrylamide gel separated the alkaline phosphatase activity from all tissues into two bands. The bands had similar electrophoretic mobilities and appeared to be qualitatively identical in corresponding tissues from Zn-deficient and control rats. 4. Zn deficiency eliminated the first band found in serum from control rats and it had selective effects on the activity of individual bands in other tissues. The major inhibitory effect was on the first bands of enzyme activity in kidney and femur, but in small intestine only the second band was affected. In liver the activity of the first band was increased and that of the second band decreased by similar amounts.

Kinetic characterization of unspecific alkaline phosphatase at different villus sites of rat jejunum. A quantitative histochemical study

A quantitative histochemical method to determine the apparent Km and Vmax values of rat intestinal unspecific alkaline phosphatase at different sites of the villi is described. Naphthol-As-Bi-phosphate (0.025-1.5 mM) is employed as substrate and Fast Blue B as coupling reagent, and the resulting azo-dye in the brush border membrane has an absorbance maximum at lambda 550 nm. The ratio between the absorbance at lambda 550 and lambda 500 nm is constant as calculated from automatically recorded spectra at different intense dye deposits. Its absorbance is a linear function of incubation time up to 3 min and thickness of the slices up to 10 micrometers both with medium (0.5 mM) and high (1.5 mM) substrate concentrations. Using the histochemical assay under comparable conditions in test tube experiments with homogenates of intestinal mucosa an app. Km of 0.26 +/- 0.081 mM (weighted regression analysis) and 0.28-0.084 mM (direct linear plotting) is determined, demonstrating an affinity to the histochemical substrate, which is about 10 times higher than for p-Nitro-phenyl-phosphate with the purified enzyme. The results obtained by scanning the total dye deposits along jejunal villi show considerable differences in enzymatic activity between single villi and an increase from the villus base up to the transition between medium and apical villus third. As well in the apical region as at the villus base saturation curves are obtained by determining the relationship between the absorbance and the substrate concentration under standard conditions (slice thickness 10 micrometers, incubation time 3 min, 37 degrees C, pH 8.3). Calculated by weighted regression analysis and direct linear plotting from the absorbance data of six female rats the medium app. kinetic data +/- SD from the jejunal villi read as follows. Apical: Km = 0.81 +/- 0.43 mM, Vmax = 3.99 +/- 1.217 absorbance units (A) and Km = 0.87 +/- 0.428 mM, Vmax = 4.02 +/- 1.191 A, respectively. Basal: Km = 0.82 +/- 0.261 mM, Vmax = 3.26 +/- 0.719 A and Km = 0.77 +/- 0.184 mM, Vmax = 3.04 +/- 0.518 AU, respectively. As demonstrated by factorial analysis of variance only Vmax is influenced by the villus position.

A histochemical study about the zonal distribution of the galactose-binding protein in rat liver

1. Dog intestinal alkaline phosphatase (IAP), an asialoglycoprotein, appeared to be a good marker for the histochemical detection of the galactose specific binding protein in cryostat sections of rat liver. 2. Binding of IAP to the receptor is optimal at neutral and slightly alkaline pH values. The binding could be inhibited by galactose and galactose containing sugars, whereas glucose and mannose did not show any effect. In contrast to fetuin itself desialylated fetuin completely inhibited IAP binding. Pretreatment of sections with phospholipase C or with trypsin inhibited IAP binding; collagenase did not show any influence. 3. The presence of the galactose-binding protein showed a distinct zonal distribution. In the area around the central vein (zone 3) the highest IAP binding capacity was found.

The differential effect of magnesium deficiency on isoenzymes of alkaline phosphatase (EC 3.1.3.1) in rat tissues

1. Alkaline phosphatase (EC 3.1.3.1) from many rat tissues was separated into two or three bands by electrophoresis on polyacrylamide gel. Ten of the bands had different electrophoretic mobilities, but some were present in more than one tissue. 2. Bands from the corresponding tissues of magnesium-deficient and control rats were qualitatively similar, but there were quantitative differences in the distribution of enzyme activity between them. 3. Mg deficiency had differential effects on the absolute activity of individual bands, but two main types of response were observed. There was an increase in the activity of the first bands from liver and kidney, the second band from femur and both bands from spleen, whereas the first band from femur, the first and second bands from intestinal mucosa and the second bands of serum, liver and kidney all decreased in activity during the deficiency. 4. The change in total alkaline phosphatase activity of a tissue during Mg deficiency depended on the ratio between the enzyme components within it.

The relations between intestinal alkaline phosphatase and carbohydrates with regard to calcium absorption

The effect of carbohydrates on calcium absorption were studied in situ following the injection of a solution containing CaCl2 (+45Ca) into the ileal loop. The increase in Ca absorption was proportional to the concentration of carbohydrates injected and could be attributed to a progressive increase in the duration of absorption. In the ileal loop, sorbitol was much more effective than L-arabinose at equal concentrations in activating absorption. Such differences in the action of these carbohydrates were also observed in vitro with alkaline phosphatase extracted from the ileum. The transphosphorylating effect of the enzyme was much more pronounced in the case of sorbitol. Since the carbohydrate is a phosphate acceptor, it might influence the duration of absorption by reducing the inhibition exerted by phosphate upon a transfer mechanism which involves phosphatase, another possibility is that carbohydrate could postpone calcium insolubility through the formation of a phosphocarbohydrate complex.

Integration of alkaline phosphatase in the intestinal brush border membrane

Alkaline phosphatase has been solubilized from porcine intestinal mucosa by two different methods: treatment of the mucosa by Emulphogen BC 720 and papain hydrolysis of enterocyte brush border membrane vesicles. Two differnt enzyme forms have been obtained by these methods. The two enzyme forms ('detergent form' and 'papain form') have been purified to homogeneity by similar techniques and exhibit closely related molecular characteristics. However, the detergent form displays a hydrophobic behaviour and aggregates in media free of detergent. The two forms can be differentiated by their electrophoretic mobility on polyacrylamide gel in the absence of sodium dodecyl sulphate. By electrophoresis on polyacrylamide gel in the presence of sodium dodecyl sulphate, it has been shown that the detergent and papain forms of alkaline phophatase are dimers consisting of two apparently identical subunits whose molecular weights are 64 000 and 61 000, respectively. The difference between these molecular weights has been attributed to the existence of a hydrophobic region in the detergent form which is present on each subunit.

Comparative study of alkaline phosphatase isoenzymes, bone histology, and skeletal radiography in dialysis bone disease

Liver, intestinal, and bone alkaline phosphatase isoenzymes were measured using heat stability and L-phenylalanine inhibition techniques in 78 patients on intermittent haemodialysis. Fifty-five patients had abnormalities in one or more of the isoenzymes. Changes in bone and intestinal alkaline phosphatase activities seemed to be related and raised liver isoenzyme activity was associated with the development of liver disease. Abnormal histological and radiological findings were better correlated with bone alkaline phosphatase levels than with total alkaline phosphatase, and serial estimations of bone isoenzyme activity were useful in assessing the response of renal osteodystrophy to treatment with a vitamin D analogue. Serum alkaline phosphatase isoenzyme measurement provides another useful and non-invasive index for monitoring metabolic bone disease in patients with chronic renal failure.

Changes in the alkaline phosphatase (EC 3.1.3.1) and inorganic pyrophosphatase (EC 3.6.1.1) activities of rat tissues during magnesium deficiency. The importance of controlling feeding pattern

1. The adoption of a meal-eating pattern of feeding by rats altered the alkaline phosphatase (EC 3.1.3.1) activity in serum and liver. It was therefore necessary to regulate the feeding pattern of both magnesium-deficient rats and control animals receiving a Mg-adequate diet in order to study the effect of the deficiency. 2. Mg deficiency decreased the activities of alkaline phosphatase and inorganic pyrophosphatase (EC 3.6.1.1) in serum, kidney and tibia, but increased them in spleen. 3. Addition of a standard concentration of exogenous Mg to tissue extracts usually increased the activity of corresponding enzymes from Mg-deficient and control rats by the same proportion, indicating that the main effect of the deficiency was on the amount of enzyme present rather than on the efficiency of its operation. 4. Certain quantitative differences in the response to exogenous Mg and the activity ratio, alkaline phosphatase:inorganic pyrophosphatase were found between tissues from Mg-deficient and control rats. The significance of these are discussed in relation to the association of the two enzymic activities with the same protein molecule, and the possible occurrence of isoenzymes.

Thiamine diphosphatase in rat small intestine

TDPase is located mostly in the proximal portion of the small intestine and its activity, like that of ALPase, decreased markedly in thiamine deficiency. The decreased enzyme activities were restored after thiamine or vitamin D3. Kinetic and other studies of the purified enzyme indicated the identity of the two enzymes.

Molecular properties of rat intestinal alkaline phosphatase

Rat intestinal alkaline phosphatase is an heterogeneous glycoprotein that contains three protein sub-forms separable by electrophoresis. The molecular weight for the glycoprotein (i.e. the average for the three sub-forms) is 157 000-160 000. Three protein sub-forms are detectable on sodium dodecyl sulphate-polyacrylamide gel electrophoresis that migrate at rates corresponding with molecular weights of 64 000, 79 000 and 92 000. Treatment of native alkaline phosphatase with 6 M guanidine - HC1 or buffer at pH 3.0 results in a product with a molecular weight of 78 000 and 70 000, respectively. Thus it is concluded that each of the three sub-forms is a dimer of identical or closely similar subunits. Limited proteolysis results in the production of new enzymically active sub-forms separable by electrophoresis. Using a bacterial protease it is possible to convert intestinal alkaline phosphatase into a form with a molecular weight of 132 000 without causing any significant change in kinetic properties. Electrophoresis of this new form on sodium dodecyl sulphate polyacrylamide gel suggests that it is composed of 66 000-dalton subunits. The native enzyme contains at least 20% by weight of carbohydrate that probably contributes to microheterogeneity of a second degree superimposed on that stemming from the presence of three protein sub-forms. Treatment with various glycosidases has no effect on electrophoretic behaviour, however. It is suggested that the three sub-forms possibly represent different stages of a maturation process that operates by limited proteolysis of a single parent protein.

Influence of certain indigenous gastrointestinal microorganisms on duodenal alkaline phosphatase in mice

Alkaline phosphatase activity was assayed in duodenal homogenates or extracts from adult specific pathogen-free (SPF) and germfree mice and gnotobiotic mice monoassociated with a Lactobacillus sp., a Bacteroides sp., or a coliform strain indigenous to SPF mice. Activity levels of the enzyme were much higher in the preparations from germfree mice than in those from the SPF controls. In the gnotobiotes monoassociated either with a freshly isolated Lactobacillus sp. or a Bacteroides sp., the levels of alkaline phosphatase activity were intermediate between the values for germfree and SPF mice. By contrast, in the gnotobiotes monoassociated with a coliform strain, alkaline phosphatase activity remained at high germfree levels. Butanol extracts of duodenal tissue from SPF mice, germfree mice, and exgermfree mice associated with an indigenous microflora from SPF mice (conventionalized) were subjected to acrylamide gel electrophoresis. A stain for alkaline phosphatase activity revealed three major bands in the gels prepared with extracts from SPF and conventionalized mice, but only two in the gels prepared with extracts from germfree mice. All three bands may have been present in the latter gels. One of the bands (the middle one) may have been obscured, however, by high activity in the slowest moving band. As determined by densitometric scanning, the slowest moving band had much higher activity in the preparations from germfree animals than in those from SPF or conventionalized mice. These findings suggest that the indigenous microbial flora affects not only quantitatively, but also qualitatively, the activity of alkaline phosphatases in the mouse intestinal mucosa.

The purification of human enterokinase by affinity chromatography and immunoadsorption. Some observations on its molecular characteristics and comparisons with the pig enzyme

A method is described for the purification of human enterokinase from accumulated duodenal fluid by affinity chromatography using p-aminobenzamidine as the ligand. Resolution was greatest when glycylglycine was substituted as the spacer arm. Purification was not a one-step procedure, and some contamination, principally by the alpha-glucosidases, remained. Their removal was completed by immunoadsorption using antisera raised to enterokinase-free material containing these enzymes, prepared as a by-product of the purification procedure. The final preparation had an activity of 4260 nmol of trypsin/min per mg and was free of other enzymic activity tested. Amino acid and sugar analyses of the highly purified enzyme indicated an acidic glycoprotein containing 57% sugar (neutral sugars 47%, amino sugars 10%). The apparent mol.wts. and Stokes radii of human and pig enterokinase were 296 000 and 316 000, and 5.65 and 5.78 nm respectively. Two isoenzymes were identified for human enterokinase and three for the pig enzyme. Human enterokinase demonstrated a resistance to reduction of disulphide linkages and to sodium dodecyl sulphate binding, which may be related to the need for it to retain its integrity in the digestive environment of the upper small intestine. Antisera to highly purified pig and human enterokinases specifically inhibited enterokinase activity. Immuno-inhibition of intestinal aminopeptidase, maltase and glucoamylase by homologous antisera was not observed.

Alkaline phosphatase isozymes of Xenopus laevis embryos and tissues

Alkaline phosphatase was obtained by treating embryos of Xenopus laevis with n-butanol at different developmental stages from gastrula to tadpole; the enzyme was also obtained from adult kidney, liver, and intestinal mucosa. Purification was carried out by gel filtration and polyacrylamide gel electrophoresis. The enzyme activity is chromatographically spearated into two peaks, with molecular weights of approximately 200,000 and 400,000. Alternatively, two groups may be characterized on the basis of their electrophoretic mobilities, which correspond to the different molecular weight classes. Effects of pH, temperature, inhibitors, and substrate concentration were studied. The kinetic and physical properties of the two alkaline phosphatase isozymes are similar, and are comparable to the properties reported for this enzyme from other vertebrates. Alkaline phosphatase activity increased sharply at the gastrula stage and reached a plateau at the late tailbud stage. During this period there was an 18-fold increase in activity.

Indentification of an intestinal sodium and calcium-dependent phosphatase stimulated by parathyroid hormone

Previous reports suggest that the site of the energy-dependent intestinal calcium transport against an electropotential and concentration gradient is located along the basal-lateral membrane of the mucosal cell. Accordingly, basal-lateral membranes were prepared from rat intestinal homogenates in order to identify the enzyme mediating this step in the transport process. An alkaline phosphatase was delineated which utilized ATP as a substrate and was dependent on both Na(-) and Ca(++) with optimum enzyme activity at 200 mM and 0.04 mM, respectively. Furthermore, the activity of the enzyme was demonstrated to decrease with the advance in age of the animal and to decrease with removal of the parathyroid glands, consistent with a decreased rate of (45)Ca release from mucosal cells under the same experimental conditions. Calcium binding to basal-lateral membrane fragments was also sodium dependent and enhanced by the prior administration of parathyroid extract. The consistent correlation between the rate of calcium transport across the basal-lateral membrane of the mucosal cell and the activity of this Na, Ca-dependent phosphatase under a variety of experimental conditions suggest that this enzyme may mediate the parathyroid hormone-sensitive active transport of calcium across the intestine.