Electron-cytochemical localization of alkaline phosphatase to G cells of Necturus maculosus antrum

Summary Electron-cytochemical localization of alkaline phosphatase activity was performed on G cells of Necturus maculosus antral mucosa. Alkaline phosphatase activity was localized to the nuclear membrane, the Golgi/endoplasmic reticulum, and the limiting membranes of G cell peptide-secretion vesicles. There was no specific localization of alkaline phosphatase activity to the plasma membrane. Treatment of the tissues with levamisole (an alkaline phosphatase inhibitor) did not markedly reduce the specific alkaline phosphatase activity. Specific lead deposition was reduced by removal of the substrate from the reaction mixture. The results from this study on N. maculosus G cells demonstrate that alkaline phosphatase activity can be found in a non-mammalian gastric endocrine cell and that specific activity was localized primarily to those intracellular structures involved with protein biosynthesis.     

Treatment of immature mice with gonadotrophins. Effects on some enzymic activities of unfractionated ovarian homogenates

Treatment of immature mice with both follicle-stimulating hormone and human chorionic gonadotrophin in vivo resulted in large increases in the specific activities of ovarian alkaline phosphatase and alkaline nucleotidase. The specific activities of other ovarian enzymes studied were not altered by gonadotrophin treatment. A simultaneous change in the Michaelis constant of ovarian alkaline phosphatase accompanied the increase in specific activity. These changes commenced 6-8h after injection of human chorionic gonadotrophin plus follicle-stimulating hormone. Injection of human chorionic gonadotrophin induced the change in Michaelis constant and increased ovarian alkaline phosphatase activity. Treatment with follicle-stimulating hormone had no effect on ovarian alkaline phosphatase. However, follicle-stimulating hormone synergistically augmented the response to human chorionic gonadotrophin. A latent period of about 24h elapsed before this augmentation was expressed. Augmentation of ovarian alkaline phosphatase was directly related to the dose of follicle-stimulating hormone at a fixed dose of chorionic gonadotrophin. No response of ovarian alkaline phosphatase was observed after treatment of immature mice in vivo with oestrogens, progesterone, growth hormone or prolactin. Unlike chorionic gonadotrophin, sheep luteinizing hormone over a wide dose range induced no response within 24h. However, a response in ovarian alkaline phosphatase was observed when sheep luteinizing hormone was administered in combination with follicle-stimulating hormone. The specific activity and K(m) of ovarian alkaline phosphatase increased during normal maturation. The Michaelis constant ceased to increase as sexual maturity was reached. The changes in alkaline phosphatase activity were of a similar magnitude to those induced by gonadotrophin treatment. It is concluded that the changes induced acutely by treatment in vivo with unphysiological doses of gonadotrophins occur in the maturing mouse under the influence of endogenous, homologous gonadotrophins at physiological concentrations.     

The relation of the soluble thiamine triphosphatase activity of various rat tissues to nonspecific phosphatases

Polyacrylamide gel electrophoresis was used to investigate the relation of the soluble thiamine triphosphatase activity of various rat tissues to other phosphatases. This technique separated the thiamine triphosphatase of rat brain, heart, kidney, liver, lung, muscle and spleen from alkaline phosphatase (EC 3.1.3.1), acid phosphatase (EC 3.1.3.2) and other nonspecific phosphatase activities. In contrast, the hydrolytic activity for thiamine triphosphate in rat intestine moved identically with alkaline phosphatase in gel electrophoresis. Thiamine triphosphatase from rat liver and brain was also separated from alkaline phosphatase and acid phosphatase by gel chromatography on Sephadex G-100. This gave an apparent molecular weight of about 30,000 and a Stokes radius of 2.5 nanometers for brain and liver thiamine triphosphatase. The intestinal thiamine triphosphatase activity of the rat was eluted from the Sephadex G-100 column as two separate peaks (with apparent molecular weights of over 200,000 and 123,000) which exactly corresponded to the peaks of alkaline phosphatase. The isoelectric point (pI) of the brain thiamine triphosphatase was 4.6 (4 degrees C). The partially purified thiamine triphosphatase from brain and liver was highly specific for thiamine triphosphate. The results suggest that, apart from the intestine, the rat tissues studied contain a specific enzyme, thiamine triphosphatase (EC 3.6.1.28). The specific enzyme is responsible for most of the thiamine triphosphatase activity in these tissues. Rat intestine contains a high thiamine triphosphatase activity but all of it appears to be due to alkaline phosphatase.     

A highly sensitive assay method for human placental alkaline phosphatase involving a monoclonal antibody bound to a paper disk

A monoclonal antibody which is specific for human placental alkaline phosphatase and does not cross-react at all with intestinal alkaline phosphatase was prepared, and a procedure for the determination of placental alkaline phosphatase activity in serum was developed involving this monoclonal antibody bound to a paper disk. The minimum amount of placental alkaline phosphatase detectable by this method is 0.0025 King-Armstrong unit. Good correlation with the heat-treatment method was obtained. Therefore this proposed method can be used as a routine clinical test for the determination of serum placental alkaline phosphatase.     

Subcellular localization and properties of pyridoxal phosphate phosphatases of human polymorphonuclear leukocytes and their relationship to acid and alkaline phosphatase

Using a novel fluorimetric assay for pyridoxal phosphate phosphatase, human polymorphonuclear leucocytes were found to exhibit both acid an alkaline activities. The neutrophils were homogenised in isotonic sucrose and subjected to analytical subcellular fractionation by sucrose density gradient centrigfugation. The alkaline pyridoxal phosphate phosphatase showed a very similar distribution to alkaline phosphatase an was located solely to the phosphasome granules. Fractionation experiments on neutrophils treated with isotonic sucrose containing digitonin and inhibitor studies with diazotised sulphanilic acid and levamisole further confirmed that both enzyme activities had similar locations and properties. Acid pyridoxal phosphate phosphatase activity was located primarily to the tertiary granule with a partial azurophil distribution. Fractionation studies on neutrophils homogenised in isotonic sucrose containing digitonin and specific inhibitor studies showed that acid pyridoxal phosphate phosphatase and acid phosphatase were not the result of a single enzyme activity, Neutrophils were isolated from control subjects, patients with chronic granulocytic leukaemia and patients in the third trimester of pregnancy. The specific activities (munits/mg protein) of alkaline pyridoxal phosphate phosphatase an alkaline phosphatase varied widely in the three groups and the alterations occurred in a parallel manner. The specific activities of acid pyridoxal phosphate phosphatase and of acid phosphatase were similar in the three groups. These results, together with the fractionation experiments and inhibition studies strongly suggest that pyridoxal phosphate is a physiological substrate for neutrophil alkaline phosphatase.     

Sub-chronic diclofenac sodium induced alterations of alkaline phosphatase activity in serum and skeletal muscle of mice

The present study has been carried on changes in activity of alkaline phosphatase in serum and gastrocnemius muscle of mice after sub-chronic use of diclofenac. Mice in experimental group received diclofenac (10 mg/kg body wt /day) for 30 days while control group received normal saline. Alkaline phosphatase was assayed in muscle and serum and its activity was localized histochemically in muscle. Results showed that diclofenac induced changes in specific activity of alkaline phosphatase at different periods of treatment variably compared to control group. Specific activity of alkaline phosphatase decreased significantly in gastrocnemius initially (48.74%), increased thereafter (132.96%) and slight decrease (13.97%) was noticed after 30 days. In serum, the specific activity of alkaline phosphatase decreased slightly after 10 days (18.78%), increased in the middle of the treatment period (132.04%) as well as showed increase (109.09%) compared to control group after 30 days stage of investigation. These findings were also confirmed by electrophoretic studies in muscle.     

Alkaline phosphatase activation and collagen synthesis in human skin fibroblasts in culture

It has been noted in regenerating wounds that alkaline phosphatase activity in fibroblasts reaches a maximum when the collagen production is greatest. Tissue culture studies were carried out to show that prednisolone phosphate, while increasing the specific activity of alkaline phosphatase in human diploid skin fibroblasts, did not affect accumulation of collagen-hydroxyproline in monolayers or media. Addition of sodium ascorbate, resulted in rapid accumulation of hydroxyproline in the culture over a 13-day interval, while alkaline phosphatase activity increased only slightly over the last 6 days. When prednisolone and ascorbate were added in combination, alkaline phosphatase activity was significantly increased: but accumulation of hydroxyproline was no greater than in cultures to which ascorbate alone was added. Activation of alkaline phosphatase induced by prednisolone phosphate does not appear to be directly related to the biosynthesis of collagen in human skin fibroblasts in tissue culture.     

A heat-stable alkaline phosphatase from Penaeus japonicus Bate (Crustacea: Decapoda): a phosphatidylinositol-glycan anchored membrane protein

1. A heat-stable alkaline phosphatase was purified from Penaeus japonicus, with a final specific activity of 21,280 U/mg of protein. 2. In polyacrylamide-gel electrophoresis under non-denaturing conditions, the purified shrimp alkaline phosphatase was found to have an identical molecular size and surface charge as the human placental enzyme. 3. By using SDS-PAGE, the monomers of shrimp alkaline phosphatase were discovered to have a Mr 55,000 but those of human placental enzyme with a Mr 70,000. Deglycosylation decreases the Mr values of the subunits to 33,000 for shrimp alkaline phosphatase. 4. The purified alkaline phosphatase from shrimp was recovered with both the attachment sites for sialic acids and phosphatidylinositol. 5. The shrimp alkaline phosphatase has an isoelectric point (pI) of 7.6 and the human placental enzyme has a pI of 4.8.     

Alkaline phosphatase in the integument of Ceratitis capitata: Developmental profile and functional properties

Electrophoretic analysis of alkaline phosphatase from the integument during development, reveals two bands of enzyme activity. One corresponding to phosphatase activity during pupation and just prior to eclosion and the other during the middle of the pupal stages. On the contrary in the haemolymph there is one band on enzyme activity through all the developmental stages. The haemolymph alkaline phosphatase band does not comigrate with any integumental enzyme band. The developmental profile of the integumental alkaline phosphatase activity has also been compared to that of the haemolymph. It was found that the pattern of activity is completely different. In the integument, two peaks of enzyme activity were found: one just prior to pupation and the other during eclosion. These two peaks do not coincide to that of haemolymph alkaline phosphatase activity. The pH optimum for both enzyme forms of third instar larvae, although broad especially for haemolymph form, was clearly in the alkaline range, with a peak at pH 8.5–9.0. The two isozymes have different affinities for the substrate tyrosine-O-phosphate. Tyrosine-O-phosphate is the preferred substrate for the integumental enzyme form with a K_m of 0.4 mM. We suggest that alkaline phosphates from the integument is specific for the hydrolysis of tyrosine-O-phosphate.     

The inhibition of alkaline phosphatase by L-p-bromotetramisole.

A levamisole analogue, the L-p-bromotetramisole is introduced as a potent inhibitor of non-specific alkaline phosphatase. Complete inhibition is achieved cytochemically at a concentration of 0.1 mM in various rat tissues except the intestine, which is not affected. The D-p-bromotetramisole does not influence the alkaline phosphatase activities. Since no effect of the inhibitor is seen on the activities of specific phosphatases, this drug is recommended also as an additive for specific phosphatase media in order to yield the specific activity only.     

Dephosphorylation of phosphoproteins of human liver plasma membranes by endogenous and purified liver alkaline phosphatases

Purified alkaline phosphatase and plasma membranes from human liver were shown to dephosphorylate phosphohistones and plasma membrane phosphoproteins. The protein phosphatase activity of the liver plasma membranes was inhibited by levamisole, a specific inhibitor of alkaline phosphatase, and by phenyl phosphonate and orthovanadate, but was relatively insensitive to fluoride (50 mM). Endogenous membrane protein phosphatase activity was optimal at pH 8.0, compared to pH 7.8 for purified liver alkaline phosphatase. Plasma membranes also exhibited protein kinase activity using exogenous histone or endogenous membrane proteins (autophosphorylation) as substrates; this activity was cAMP-dependent. Autophosphorylation of plasma membrane proteins was apparently enhanced by phenyl phosphonate, levamisole, or orthovanadate. The dephosphorylation of phosphohistones by protein phosphatase 1 was not inhibited by levamisole but was inhibited by fluoride. Inhibition of endogenous protein phosphatase activity by orthovanadate during autophosphorylation of plasma membranes could be reversed by complexation of the inhibitor with (R)-(-)-epinephrine, and the dephosphorylation that followed was levamisole-sensitive. Neither plasma membranes nor purified liver alkaline phosphatase dephosphorylated glycogen phosphorylase a. These results suggest that the increased [32P]phosphate incorporation by endogenous protein kinases into the membrane proteins is due to inhibition of alkaline phosphatase and that the major protein phosphatase of these plasma membranes is alkaline phosphatase.     

The preparation of monoclonal antibodies to human bone and liver alkaline phosphatase and their use in immunoaffinity purification and in studying these enzymes when present in serum.

1. Liver and bone alkaline phosphatase isoenzymes were solubilized with the zwitterionic detergent sulphobetaine 14, and purified to homogeneity by using a monoclonal antibody previously raised against a partially-purified preparation of the liver isoenzyme. Both purified isoenzymes had a specific activity in the range 1100-1400 mumol/min per mg of protein with a subunit Mr of 80,000 determined by SDS/polyacrylamide gel electrophoresis. Butanol extraction instead of detergent solubilization, before immunoaffinity purification of the liver enzyme, resulted in the same specific activity and subunit Mr. The native Mr of the sulphobetaine 14-solubilized enzyme was consistent with the enzyme being a dimer of two identical subunits and was higher than that of the butanol-extracted enzyme, presumably due to the binding of the detergent micelle. 2. Pure bone and liver alkaline phosphatase were used to raise further antibodies to the two isoenzymes. Altogether, 27 antibody-producing cell lines were cloned from 12 mice. Several of these antibodies showed a greater than 2-fold preference for bone alkaline phosphatase in the binding assay used for screening. No antibodies showing a preference for liver alkaline phosphatase were successfully cloned. None of the antibodies showed significant cross-reaction with placental or intestinal alkaline phosphatase. Epitope analysis of the 27 antibodies using liver alkaline phosphatase as antigen gave rise to six groupings, with four antibodies unclassified. The six major epitope groups were also observed using bone alkaline phosphatase as antigen. 3. Serum from patients with cholestasis contains soluble and particulate forms of alkaline phosphatase. The soluble serum enzyme had the same size and charge as butanol-extracted liver enzyme on native polyacrylamide-gel electrophoresis. Cellulose acetate electrophoresis separated the soluble and particulate serum alkaline phosphatases as slow- and fast-moving forms respectively. In the presence of sulphobetaine 14 all the serum enzyme migrated as the slow-moving form on cellulose acetate electrophoresis. Monoclonal anti-(alkaline phosphatase) immunoadsorbents did not bind the particulate form of alkaline phosphatase in cholestatic serum but bound the soluble form. In the presence of sulphobetaine 14 all the cholestatic serum alkaline phosphatase bound to the immunoadsorbents. 4. The electrophoretic and immunological data are consistent with both particulate and soluble forms of alkaline phosphatase in cholestatic serum being derived from the hepatocyte membrane.     

The effect of bromodeoxyuridine and dibutyryl cyclic AMP on the induction of placental alkaline phosphate in human choriocarcinoma cells.

The effect of 5-bromo-2'-deoxyuridine (BrdUrd) and dibutyryl cyclic AMP (Bt2cAMP) on the expression of the placental isoenzyme of human alkaline phosphatase was examined in BeWo choriocarcinoma cells. By using a combination of specific immunoprecipitation and polyacrylamide-gel electrophoresis of cells labelled either metabolically with [35S]methionine or cell-surface-labelled with 125I, both BrdUrd (5 micrograms/ml) and 1 mM-Bt2cAMP were shown to result in the enhanced accumulation of a specific protein. This protein has immunochemical identity and co-electrophoreses with placental alkaline phosphatase in two-dimensional gels. These results clearly demonstrate that the induction of placental alkaline phosphatase activity in choriocarcinoma cells treated with these agents is a consequence of the accumulation of specific enzyme protein rather than of altered catalytic activity.     

Cytochemical studies on the localization of alkaline phosphatase and HCO-3-activated adenosine triphosphatase in the brush border membrane of rat duodenal enterocytes

Cytochemical techniques were used to demonstrate, with appropriate controls, alkaline phosphatase and HCO-3-activated adenosine triphosphatase (ATPase) in rat duodenal brush border microvillus membranes. Intense activity of ecto-alkaline phosphatase activity was demonstrated with 2-glycerophosphate as substrate. Although biochemical assays suggested that L-phenylalanine inhibited both alkaline phosphatase and HCO-3-activated ATPase, cytochemical studies indicated that there was marked inhibition of alkaline phosphatase revealing a specific HCO-3-activated ATPase on the inner aspect of the microvillus membrane. While it is tempting to suggest that this HCO-3-activated ATPase is implicated in active bicarbonate secretion by the duodenum, decisive identification is not yet possible.     

5-Bromo-2'-deoxyuridine induces placental alkaline phosphatase biosynthesis in cultured choriocarcinoma cells

5-Bromo-2'-deoxyuridine (BrdUrd) stimulated the biosynthesis and hence increased the activity of placental alkaline phosphatase in choriocarcinoma cells. While BrdUrd had no effect on the rate of degradation or processing of placental alkaline phosphatase, it increased the rate of phosphatase synthesis. The stimulation of enzyme activity could be completely accounted for by the increase in alkaline phosphatase protein. Both control and BrdUrd-induced cells contained polypeptides of 61,500 and 64,500 Da, identified as the precursor and fully processed forms of placental alkaline phosphatase monomer. The half-life of this enzyme monomer in both control and BrdUrd-treated cells was estimated to be 36 h. BrdUrd induced a specific increase in the placental alkaline phosphatase mRNA leading to the observed enhancement of biosynthesis. The continued rise in alkaline phosphatase biosynthesis in BrdUrd-induced cells following BrdUrd removal indicated that this analog acted by incorporation into DNA.     

The presence and activity in normal and regenerating rat liver postmicrosomal supernatant fraction of an enzyme with properties similar to those of membrane-bound 5''-nucleotidase.

An alkaline 5'-nucleotidase with properties similar to those of membrane-bound 5'-nucleotidase was recovered in soluble form in the postmicrosomal supernatant fraction (cytosol) of rat liver. The enzyme seems to constitute a quantitatively distinct fraction, since the activity in postmicrosomal supernatants was increased by a further 10% by additional homogenization of livers. Lysosomal acid phosphatase activity increased similarly, whereas other membrane-bound marker enzymes alkaline phosphatase, phosphodiesterase I and glucose-6-phosphatase showed no increase when homogenization of liver tissue was continued. Gel-permeation chromatography and pH-dependence studies indicated that enzyme activity in the supernatant fraction with 0.3 mM-UMP or -AMP as substrate at pH 8.1 was about 85 or 100% specific respectively. In regenerating liver the enzyme recovered in soluble form showed decreased specific activity, in contrast with alkaline phosphatase measured for comparison. The nucleotidase activity per mg of cytosolic protein was 2.1 nmol/min with AMP as substrate. The total activity measured in the postmicrosomal supernatant was 1.5% of the homogenate activity measured in the presence of detergent.     

Tyrosine kinase inhibitors reverse butyrate stimulation of human Caco-2 intestinal epithelial cell alkaline phosphatase but not butyrate promotion of dipeptidyl dipeptidase

Short chain fatty acids such as sodium butyrate are concentrated in the colonic lumen and may protect against colon carcinogenesis by maintaining colonocytic differentiation, but the mechanisms by which they act are not fully understood. It has recently been suggested that short chain fatty acids modulate cellular tyrosine kinase activity in addition to altering chromatin structure via regulation of histone acetylation and DNA methylation. Therefore, the authors evaluated the influence of tyrosine kinase inhibition on the effects of 10 mM butyrate on human Caco-2 intestinal epithelial differentiation, using alkaline phosphatase and dipeptidyl dipeptidase specific activity as markers of differentiation, and two tyrosine kinase inhibitors, of different mechanisms of action and different effects on Caco-2 brush border enzyme specific activity, to block tyrosine kinase activity. As expected, butyrate stimulated both alkaline phosphatase and dipeptidyl dipeptidase specific activity. The tyrosine kinase inhibitors prevented, and indeed one inhibitor reversed the effects of butyrate on alkaline phosphatase specific activity. However, tyrosine kinase inhibition did not prevent butyrate stimulation of dipeptidyl dipeptidase specific activity. Different pathways are likely to regulate the effects of butyrate on expression of these two brush border enzymes. Butyrate stimulation of alkaline phosphatase, but not dipeptidyl dipeptidase, may involve tyrosine phosphorylation signaling.     

Alkaline phosphatase in HeLa cells. Stimulation by phospholipase A2 and lysophosphatidylcholine.

Treatment of homogenates and plasma membrane preparations from HeLa cells with phospholipase A2 (EC 3.1.1.4) caused a 50% increase in activity of membrane-associated alkaline phosphatase. Lysophosphatidylcholine, dispersed in 0.15 M KCl, affected alkaline phosphatase in a similar fashion by releasing the enzyme from particulate fractions into the incubation medium and by elevating its specific activity. Higher concentrations of lysophosphatidylcholine solubilized additional protein from particulate fractions but did not further increase the specific activity of the released alkaline phosphatase. Particulate fractions from HeLa cells were exposed to the effects of liposomes prepared from lysophosphatidylcholine and cholesterol. The ratio of particulate protein/lysophosphatidylcholine (by weight) required for optimal activation of alkaline phosphatase was one. Kinetic studies indicated that phospholipase A2 and lysophosphatidylcholine enhanced the apparent V of the enzyme but did not significantly alter its apparent Km. The increased release of alkaline phosphatase from the particulate matrix by lysophosphatidylcholine was confirmed by disc electrophoresis. The release of the enzyme by either phospholipase A2 or by lysophosphatidylcholine appeared to be followed by the formation of micelles that contained lysophosphatidylcholine. The new complexes had relatively less cholesterol and more lysophosphatidylcholine than the native membranes. The possibility that lysophosphatidylcholine formed a lipoprotein complex with the solubilized alkaline phosphatase was indicated by a break point in the Arrhenius plot which was evident only in the lysophosphatidylcholine-solubilized enzyme but could not be demonstrated in alkaline phosphatase that had been released with 0.15 M KCl alone.     

The inhibition of alkaline phosphatase by l-p-bromotetramisole

Summary A levamisole analogue, the l-p-bromotetramisole is introduced as a potent inhibitor of non-specific alkaline phosphatase.Complete inhibition is achieved cytochemically at a concentration of 0.1 mM in various rat tissues except the intestine, which is not affected. The d-p-bromotetramisole does not influence the alkaline phosphatase activities.Since no effect of the inhibitor is seen on the activities of specific phosphatases, this drug is recommended also as an additive for specific phosphatase media in order to yield the specific activity only.