Rat intestinal alkaline phosphatase. A microheterogeneous series of glycoproteins

In vitro drug absorption models. I. Brush border membrane vesicles, isolated mucosal cells and everted intestinal rings: characterization and salicylate accumulation

Brush border membrane vesicles, isolated mucosal cells and everted rings from rat intestine were compared for their suitability for drug uptake studies. Vesicles from brush border membranes were judged to be metabolically and morphologically functional on the basis of biochemical and microscopic criteria. With the use of a collagenase-vascular-perfusion method, populations of villus, mid villus and crypt cells were separated. An alternative approach that is based on an EDTA-dissociation procedure afforded fractions enriched in villus and crypt cells. Although several enzymatic and metabolic activities of these two cell preparations were comparable, cell viability based on the Trypan Blue dye exclusion test, ultrastructural appearance and glucose uptake more closely conformed to in vivo values for cells isolated according to the EDTA-dissociation method. These cells were chosen as a model for drug transport investigation. The morphological and functional integrity of everted rings was verified by histological examination, extracellular space estimation and assessment of glucose transport ability. Sodium salicylate uptake studies using brush border membrane vesicles and isolated mucosal cells were highly variable, whereas everted segments exhibited good reproducibility in uptake experiments. Time dependence of salicylate uptake was demonstrated with membrane vesicles and everted rings. Time dependence was not observed in mucosal cell uptake studies, probably because of the time required to separate the cells from the incubation solution. Based on ease of preparation, technical aspects of in vitro incubation and reproducibility of results, everted intestinal rings were considered to be a good potential model for in vivo drug absorption. Brush border membrane vesicles were generally regarded as unacceptable because of variations after storage and between experiments. Isolated cells offered certain advantages, but the utility of cells as an in vitro model remains equivocal.

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.

Alkaline phosphatase of basal lateral and brush border plasma membranes from intestinal epithelium

The alkaline phosphatase present on isolated brush border and basal lateral membranes of rat duodenal epithelium were examined by means of a variety of biochemical assays and physical methods. The two alkaline phosphatases have similar pH optima of 9.6--9.8, similar substrate km's for p-nitrophenyl phosphate (PNPP) of 71 micromolar, similar responses to the inhibitors 2-mercaptoethanol, theophylline, phenylalanine, and ethylenediaminetetraacetic acid (EDTA), similar sensitivities to calcium, magnesium, zinc, sodium, and potassium, and similar insensitivities to digestion with trypsin of papain. The two enzymes also exhibit similar molecular weights on SDS-polyacrylamide gels in the range 124,000--150,000, and both enzymes show an Rf value of 0.092 on Triton X-100 polyacrylamide gels, indicating similar intrinsic charges. The Vmax of the brush border enzyme is ten times greater than that of the basal lateral enzyme, 140 mumoles/mg-h as opposed to 14 mumoles/mg-h. The differences in Vmax are a reflection of the known distribution of alkaline phosphatase in rat duodenum, there being more alkaline phosphatase activity present on the brush border than on the basal lateral surface. One other major difference was observed between the two enzymes, the stimulation of the basal lateral and not the brush border alkaline phosphatase by SDS, Triton X-100, or cholate. We conclude that the enzymes are very similar to one another and probably perform similar membrane functions.

Effect of prenatal and neonatal pantothenic acid deficiency on rat intestinal phosphatases

Alkaline phosphatase activity was increased in the distal part of the small intestine of pantothenic acid deficient neonatal rats, while acid phosphatase activity was slightly increased and protein concentration was decreased throughout the small intestine. The growth and maturation of the distal part of the small intestine were retarded more severely than in the proximal part.

Induction of alkaline phosphatase in Escherichia coli. Effect of phenethyl alcohol

Induction of alkaline phosphatase, an enzyme located in the periplasmic region of Escherichia coli, was inhibited by phenethyl alcohol, an agent believed to alter the cell membrane structure. Studies to elucidate mechanism of this inhibition showed that while phenethyl alcohol arrested the incorporation of [3H]leucine into active alkaline phosphatase, it did allow substantial incorporation of the label into inactive monomer subunits of the enzyme. These results suggest that phenethyl alcohol may not interfere with the de novo synthesis of monomer subunits of the enzyme but arrest conversion of these into active dimer enzyme presumably by its primary action on the cell membrane structure.

Induction of alkaline phosphatase in Escherichia coli: effect of procaine hydrochloride

The effect of procaine hydrochloride, an anesthetic known to alter membrane structure, on the induced formation of alkaline phosphatase, a periplasmic enzyme, in Escherichia coli was investigated. Procaine hydrochloride specifically arrested the appearance of active alkaline phosphatase while permitting the induction of another enzyme, beta-galactosidase, which is internally localized. Evidence has been obtained to show that procaine hydrochloride does not arrest synthesis of inactive monomer subunits of the enzyme, indicating that the drug interferes in the conversion of monomer subunits to an active dimer enzyme.

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.

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.