The influence of metal ions on the orthophosphatase and inorganic pyrophosphatase activities of human alkaline phosphatase

1. The differential effects of adding Zn(2+) and Mg(2+) on the orthophosphatase and inorganic pyrophosphatase activities of human intestinal alkaline phosphatase were studied. 2. In the presence of excess of Zn(2+), inorganic pyrophosphatase activity is inhibited. At higher concentrations of pyrophosphate, hydrolysis of this substrate takes place, but is inhibited competitively by the Zn(2+)-pyrophosphate complex. This complex also acts as a competitive inhibitor of orthophosphate hydrolysis. 3. Excess of Mg(2+) also inhibits pyrophosphatase action by removal of substrate; at low concentrations, this ion activates pyrophosphatase, as is the case with orthophosphatase. 4. It is concluded that, when interactions between metal ions and pyrophosphate are taken into account, the effects of these ions are consistent with the view that alkaline phosphatases possess both orthophosphatase and inorganic pyrophosphatase activities.     

Energy transduction at the catalytic site of enzymes: hydrolysis of phosphoester bonds and synthesis of pyrophosphate by alkaline phosphatase

Alkaline phosphatase from mouse intestinal epithelial cells catalyzes the synthesis of pyrophosphate from Pi during hydrolysis of either glucose 6-phosphate, ATP, ADP, inorganic pyrophosphate or p-nitrophenylphosphate. The rate of pyrophosphate synthesis is increased by MgCl2 and by decreasing the pH of the medium from 8.5 to 6.0. The data presented indicate that at the catalytic site of alkaline phosphatase the energies of hydrolysis of the phosphoserine residue and of pyrophosphate are different from those measured in aqueous solutions.     

Inhibition of the orthophosphatase and pyrophosphatase activities of human alkaline-phosphatase preparations

1. Purified human liver and small-intestinal alkaline orthophosphatases release inorganic phosphate at appreciable rates from a variety of organic pyrophosphate substrates. 2. The pyrophosphatase action is inhibited by Mg²⁺ ions at concentrations that activate the hydrolysis of orthophosphate substrates by these enzymes. 3. The results of mixed-substrate experiments, denaturation studies with heat or urea and starch-gel electrophoresis suggest that both orthophosphatase and pyrophosphatase activities are, in each preparation, properties of a single enzyme. 4. Intestinal phosphatase shows greater pyrophosphatase activity relative to orthophosphatase than the liver enzyme.     

Organic pyrophosphates as substrates for human alkaline phosphatases

1. Purified human liver and small-intestinal alkaline orthophosphatases release inorganic phosphate at appreciable rates from a variety of organic pyrophosphate substrates. 2. The pyrophosphatase action is inhibited by Mg²⁺ ions at concentrations that activate the hydrolysis of orthophosphate substrates by these enzymes. 3. The results of mixed-substrate experiments, denaturation studies with heat or urea and starch-gel electrophoresis suggest that both orthophosphatase and pyrophosphatase activities are, in each preparation, properties of a single enzyme. 4. Intestinal phosphatase shows greater pyrophosphatase activity relative to orthophosphatase than the liver enzyme.     

The cell surface associated phosphatase activity of Mycobacterium bovis BCG is not regulated by environmental inorganic phosphate

Non-specific phosphomonoesterase activities (alkaline phosphatase (EC 3.1.3.1) and acid phosphatase (EC 3.1.3.2)) were examined at the cell surface of Mycobacterium bovis BCG. Using p-nitrophenylphosphate as the substrate, peaks of phosphatase activity were detected at pH 6.0, pH 10.0 and pH 12.0, suggesting the presence of one acid phosphatase and two alkaline phosphatases with distinct optimum pH values. Contrary to the situation observed in several other microorganisms, the expression of these enzymes is not regulated by the environmental inorganic phosphate concentration.     

32P-labeling of bovine tryptophanyl-tRNA synthetase with [32P]pyrophosphate

The covalent derivative of the tryptophanyl-tRNA synthetase obtained under the action of³²PP_i contains one mole of the covalently bound pyrophosphate (or 2 moles of orthophosphate) per mole of dimeric enzyme. Dephosphorylation with alkaline phosphatase causes practically no changes of enzymatic activity although the enzyme looses its ability to bind PP_i.Enzymes tryptophanyl-tRNA synthetase (EC 6.1.1.2), alkaline phosphatase (EC 3.1.3.1), inorganic pyrophosphatase (EC 3.6.1.1)     

Alkaline Phosphatase and Other Hydrolyases Produced by Cenococcum graniforme, an Ectomycorrhizal Fungus

Cell extracts of Cenococcum graniforme have been found to contain the following hydrolytic enzymes: protease, esterase, alpha-d-galactopyranosidase, beta-d-galactopyranosidase, alpha-d-mannopyranosidase, beta-d-xylopyranosidase, alpha-d-glucopyranosidase, beta-d-glucopyranosidase, and alkaline phosphatase. Sulfatase, inorganic pyrophosphatase, and beta-d-mannopyranosidase were not detected in the extracts. beta-d-Xylopyranosidase and alpha-d-mannopyranosidase were most active in the neutral pH range, protease and phosphatase were most active in the alkaline pH range, and other enzymes were most active in the acidic pH range. These enzymes showed a high association with cell wall material, and the release of enzymes from the cells into the culture fluid appeared to occur only when the cells were undergoing autolysis. Alkaline phosphatase in C. graniforme is a constitutive enzyme, and examination of the alkaline phosphatase following a purification of 265-fold produced the following characteristics: pH optimum of 9.5, M(r) of 60,000, K(m) of 2.1 x 10 M for p-nitrophenylphosphate, and activation energy for hydrolysis of the substrate at 9.9 kcal (1 cal = 4.184 J)/mol.     

Alkaline inorganic pyrophosphatase activity of mammalian-cell alkaline phosphatase

Alkaline phosphatase prepared from mammalian cell cultures was found to have alkaline inorganic pyrophosphatase activity. Both of these activities appear to be associated with a single protein, as demonstrated by: (1) concomitant purification of alkaline phosphatase and alkaline inorganic pyrophosphatase; (2) proportional precipitation of alkaline phosphatase and inorganic pyrophosphatase activities by titrating constant amounts of an enzyme preparation with increasing concentration of antibody; (3) immune electrophoresis, which showed that precipitin bands that have alkaline phosphatase activity also have pyrophosphatase activity; (4) inhibition of pyrophosphatase activity by cysteine, an inhibitor of alkaline phosphatase activity; (5) similar subcellular localization of the two enzyme activities as demonstrated by histochemical methods; (6) hormonal and substrate induction of alkaline phosphatase activity in mammalian cell cultures, which produced a nearly parallel rise in inorganic pyrophosphatase activity.     

The Effect of Pyrophosphate Analogues on the Activity of the Inorganic Pyrophosphatase from Escherichia coli

The effect of inorganic pyrophosphate analogues on the enzymic activity of inorganic pyrophosphatase from E. coli was studied. Hypophosphoric and diphosphonic acids were shown to inhibit inorganic pyrophosphatase, whereas pyrophosphorous acid exerts almost no effect on the hydrolysis of inorganic pyrophosphate.     

Studies on matrix vesicles isolated from chick epiphyseal cartilage. Association of pyrophosphatase and ATPase activities with alkaline phosphatase.

Fractions composed primarily of cells (Fraction I), membrane fragments (Fraction II) and matrix vesicles (Fraction III) were isolated from chick epiphyseal cartilage. The characteristics of the alkaline phosphatase (EC 3.1.3.1), pyrophosphatase (EC 3.6.1.1) and ATPase (EC 3.6.1.3) activities in the matrix vesicle fraction were studied in detail. Mg-2-+ was not absolutely essential to any of the activities, but at low levels was stimulatory in all cases. Higher concentrations inhibited both pyrophosphatase and ATPase activities. Both the stimulatory and inhibitory effects were pH-dependent. Ca-2-+ stimulated all activities weakly in the absence of Mg-2-+. However, when Mg-2-+ was present, Ca-2-+ was slightly inhibitory. Thus, none of the activities appear to have a requirement for Ca-2-+, and hence would not seem to be involved with active Ca-2-+ transport in the typical manner. The distribution of alkaline phosphatase, pyrophosphatase, and Mg-2-+ ATPase activities among the various cartilage fractions was identical, and concentrated primarily in the matrix vesicles. Conversely, the highest level of (Na-+ + K-+)-ATPase activity was found in the cell fraction. All activites showed nearly identical sensitivities to levamisole (4 - 10-3 M) which caused nearly complete inhibition of alkaline phosphatase and pyrophosphatase. About 10-15% of the ATPase activity was levamisole-insensitive. The data are consistent with the concept that the Mg-2-+-ATPase and pyrophosphatase activities of matrix vesicles stem from one enzyme, namely, alkaline phosphatase.     

P5L mutation in Ank results in an increase in extracellular inorganic pyrophosphate during proliferation and nonmineralizing hypertrophy in stably transduced ATDC5 cells

Ank is a multipass transmembrane protein that regulates the cellular transport of inorganic pyrophosphate. In the progressive ankylosis (ank) mouse, a premature termination mutation at glutamic acid 440 results in a phenotype characterized by inappropriate deposition of basic calcium phosphate crystals in skeletal tissues. Mutations in the amino terminus of ANKH, the human homolog of Ank, result in familial calcium pyrophosphate dihydrate deposition disease. It has been hypothesized that these mutations result in a gain-of-function with respect to the elaboration of extracellular inorganic pyrophosphate. To explore this issue in a mineralization-competent system, we stably transduced ATDC5 cells with wild-type Ank as well as with familial chondrocalcinosis-causing Ank mutations. We evaluated the elaboration of inorganic pyrophosphate, the activity of pyrophosphate-modulating enzymes, and the mineralization in the transduced cells. Expression of transduced protein was confirmed by quantitative real-time PCR and by ELISA. Levels of inorganic pyrophosphate were measured, as were the activities of nucleotide pyrophosphatase phosphodiesterase and alkaline phosphatase. We also evaluated the expression of markers of chondrocyte maturation and the nature of the mineralization phase elaborated by transduced cells. The cell line expressing the proline to leucine mutation at position 5 (P5L) consistently displayed higher levels of extracellular inorganic pyrophosphate and higher phosphodiesterase activity than the other transduced lines. During hypertrophy, however, extracellular inorganic pyrophosphate levels were modulated by alkaline phosphatase activity in this cell system, resulting in the deposition of basic calcium phosphate crystals only in all transduced cell lines. Cells overexpressing wild-type Ank displayed a higher level of expression of type X collagen than cells transduced with mutant Ank. Other markers of hypertrophy and terminal differentiation, such as alkaline phosphatase, osteopontin, and runx2, were not significantly different in cells expressing wild-type or mutant Ank in comparison with cells transduced with an empty vector or with untransduced cells. These results suggest that the P5L Ank mutant is capable of demonstrating a gain-of-function with respect to extracellular inorganic pyrophosphate elaboration, but this effect is modified by high levels of expression of alkaline phosphatase in ATDC5 cells during hypertrophy and terminal differentiation, resulting in the deposition of basic calcium phosphate crystals.     

P5L mutation in Ank results in an increase in extracellular inorganic pyrophosphate during proliferation and nonmineralizing hypertrophy in stably transduced ATDC5 cells

Ank is a multipass transmembrane protein that regulates the cellular transport of inorganic pyrophosphate. In the progressive ankylosis (ank) mouse, a premature termination mutation at glutamic acid 440 results in a phenotype characterized by inappropriate deposition of basic calcium phosphate crystals in skeletal tissues. Mutations in the amino terminus of ANKH, the human homolog of Ank, result in familial calcium pyrophosphate dihydrate deposition disease. It has been hypothesized that these mutations result in a gain-of-function with respect to the elaboration of extracellular inorganic pyrophosphate. To explore this issue in a mineralization-competent system, we stably transduced ATDC5 cells with wild-type Ank as well as with familial chondrocalcinosis-causing Ank mutations. We evaluated the elaboration of inorganic pyrophosphate, the activity of pyrophosphate-modulating enzymes, and the mineralization in the transduced cells. Expression of transduced protein was confirmed by quantitative real-time PCR and by ELISA. Levels of inorganic pyrophosphate were measured, as were the activities of nucleotide pyrophosphatase phosphodiesterase and alkaline phosphatase. We also evaluated the expression of markers of chondrocyte maturation and the nature of the mineralization phase elaborated by transduced cells. The cell line expressing the proline to leucine mutation at position 5 (P5L) consistently displayed higher levels of extracellular inorganic pyrophosphate and higher phosphodiesterase activity than the other transduced lines. During hypertrophy, however, extracellular inorganic pyrophosphate levels were modulated by alkaline phosphatase activity in this cell system, resulting in the deposition of basic calcium phosphate crystals only in all transduced cell lines. Cells overexpressing wild-type Ank displayed a higher level of expression of type X collagen than cells transduced with mutant Ank. Other markers of hypertrophy and terminal differentiation, such as alkaline phosphatase, osteopontin, and runx2, were not significantly different in cells expressing wild-type or mutant Ank in comparison with cells transduced with an empty vector or with untransduced cells. These results suggest that the P5L Ank mutant is capable of demonstrating a gain-of-function with respect to extracellular inorganic pyrophosphate elaboration, but this effect is modified by high levels of expression of alkaline phosphatase in ATDC5 cells during hypertrophy and terminal differentiation, resulting in the deposition of basic calcium phosphate crystals.     

Kinetics and thermodynamics of catalysis by the inorganic pyrophosphatase of Escherichia coli in both directions

Combined evidence obtained from the measurements of pyrophosphate hydrolysis and synthesis, oxygen exchange between phosphate and water, enzyme-bound pyrophosphate formation and Mg2+ binding enabled us to deduce the overall scheme of catalysis by Escherichia coli inorganic pyrophosphatase in the presence of Mg2+. We determined the equilibrium constants for Mg2+ binding to various enzyme species and forward and reverse rate constants for the four steps of the catalytic reaction, namely, binding/release of PPi, hydrolysis/synthesis of PPi and successive binding/release of two Pi molecules. Catalysis by the E. coli enzyme in both directions, in contrast to baker's yeast pyrophosphatase, occurs via a single pathway, which requires the binding of Mg2+ to the sites of four types. Three of them can be filled in the absence of the substrates, and the affinity of one of them to Mg2+ is increased by two orders of magnitude in the enzyme-substrate complexes. The distribution of 18O-labelled phosphate isotopomers during the exchange indicated that hydrolysis of pyrophosphate in the active site is appreciably reversible. The equilibrium constant for this process estimated from direct measurements is 5.0. The ratio of the maximal velocities of pyrophosphate hydrolysis and synthesis is 69. The rate of the synthesis is almost entirely determined by the rate of the release of pyrophosphate from the enzyme. In the hydrolytic reaction, enzyme-bound pyrophosphate hydrolysis and successive release of two phosphate molecules proceed with nearly equal rate constants.     

Inhibition studies of alkaline phosphatase in hard tissue-forming cells.

The effects of the alkaline phosphatase inhibitors levamisole and R 8231 on p-nitro-phenylphosphatase, inorganic pyrophosphatase and adenosine triphosphatase (ATPase) activities in dentingenically active odontoblasts were studied. The p-nitrophenylphosphatase and inorganic pyrophosphatase activities were inhibited, while 40% of the ATP-splitting enzyme activity remained under the assay condition used. This finding, togeather with earlier studies, indicates that at least two different phosphatase are active at alkaline pH in hard tissue-forming cells; on nonspecific alkaline phosphatase and one specific ATPase. The ATPase activity is uninfluenced by ouabain and ruthenium red and is activated by Ca-2+ ions.     

Enzymatic characterization of the chondrocytic alkaline phosphatase isolated from bovine fetal epiphyseal cartilage.

Purified chondrocytic alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) from bovine fetal epiphyseal cartilage hydrolyzes a variety of phosphate esters as well as ATP and inorganic pyrophosphate. Optimal activities for p-nitrophenyl phosphate, ATP and inorganic pyrophosphate are found at pH 10.5, 10.0 and 8.5, respectively. The latter two substrates exhibit substrate inhibition at high concentrations. p-Nitrophenyl phosphate demonstrates decreasing pH optima with decreasng substrate concentration. Heat inactivation studies indicate that both phosphorolytic and pyrophosphorolytic cleavage occur at the same site on the enzyme. Mg2+ (0.1-10.0 mM) and Mn2+ (0.01-0.1 mM) show a small stimulation of p-nitrophenyl phosphate-splitting activity at pH 10.5. Levamisole, Pi, CN-, Zn2+ and L-phenylalanine are all reversible inhibitors of the phosphomonoesterase activity. Pi is a competitive inhibitor with a Ki of 10.0 mM. Levamisole and Zn2+ are potent non-competitive inhibitors with inhibition constants of 0.05 and 0.04 mM, respectively. The chondrocytic alkaline phosphatase is inhibited irreversibly by Be2+, EDTA, EGTA, ethane-1-hydroxydiphosphonate, dichloromethane diphosphonate, L-cysteine, phenyl-methylsulfonyl fluoride, N-ethylmaleimide and iodoacetamide. NaCL, KCL and Na2SO4 at 0.5-1.0 M inhibit the enzyme. At pH 8.5, the cleavage of inorganic pyrophosphate (pyrophosphate phosphohydrolase, EC 3.6.1.1) by the chondrocytic enzyme is slightly enhanced by low levels of Mg2+ and depressed by concentrations higher than 1mM. Ca2+ show only inhibition. Similar effects of Mg2+ and Ca2+ on the associated ATPase (ATP phosphohydrolase, EC 3.1.6.3) activity were observed. Arrhenius studies using p-nitrophenyl phosphate and AMP as substrates have accounted for the ten-fold difference in V in terms of small differences in both the enthalpies and entropies of activation which are 700 cal/mol and 2.3 cal/degree per mol, respectively.     

Alkaline phosphatases in fixed plant cells

Alkaline phosphatase activity in fixed plant cells has now been demonstrated cytochemically. Presumably cytochemical findings on plant alkaline phosphatases had been lacking because glycerophosphate, which is not hydrolyzed by fixed plant cells, had been used as the substrate.Alkaline phosphatase activity in the onion and corn nuclei has been compared with the activity in rat tissues. In the plant tissues, hydrolysis of phosphates was demonstrated when the substrates guanylic acid, adenosine diphosphate, adenosine triphosphoric acid, diphosphopyridine nucleotide, hexosediphosphates and inorganic pyrophosphate and metaphosphate were used. When the substrates glycerophosphate, adenylic acid and hexosemonophosphates were used, hydrolysis was not found. In the animal tissues however, hydrolysis was demonstrated of all organic phosphoesters employed and of sodium metaphosphate but not the hydrolysis of sodium pyrophosphate.One alkaline phosphatase found in the fixed plant tissues specifically hydrolyzed guanylic acid but no other nucleotide and one specifically hydrolyzed metaphosphate to orthophosphate.The enzymes in both plant and animal cells which hydrolyzed metaphosphates and pyrophosphates were found to require magnesium ions for their activity and to be inhibited by fluoride ions.“Alkaline, phosphatase,” so intimately associated with the chromatin in the nucleus, is postulated to be not just one enzyme but a number of enzymes.     

The effect of pyrophosphate analogues on the inorganic pyrophosphatase from Escherichia coli

The effect of inorganic pyrophosphate analogues on the enzymic activity of inorganic pyrophosphatase from E. coli was studied. Hypophosphoric and diphosphonic acids were shown to inhibit inorganic pyrophosphatase, whereas pyrophosphorous acid exerts almost no effect on the hydrolysis of inorganic pyrophosphate. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 6; see also http://www.maik.ru.     

Zn2+-Dependent Acid Inorganic Pyrophosphatase Activity as Related to Other Pyrophosphatases in Oryza sativa

Acid inorganic pyrophosphatase on the one hand, and Mg²⁺-dependent alkaline inorganic pyrophosphatase and Zn²⁺-dependent acid inorganic pyrophosphatase on the other hand showed opposite trends in their activities in rice (Oryza sativa L. cv. Ratna) seedlings grown in dark and sun. The opposite trends in their activities were also noted in rice seedlings grown from gamma-irradiated seeds and in detached rice leaves floated on water in dark. The ratios of Mg²⁺ dependent alkaline inorganic pyrophosphatase/acid inorganic pyrophosphatase and Zn²⁺-dependent acid inorganic pyrophosphatase/acid inorganic pyrophosphatase changed significantly in response to the above physical treatments, but the ratio of Mg²⁺ dependent alkaline inorganic pyrophosphatase/Zn²⁺ dependent acid inorganic pyrophosphatase remained relatively stable. The conclusion is that Zn²⁺-dependent acid inorganic pyrophosphatase activity is the same as that of Mg²⁺-dependent alkaline inorganic pyrophosphatase and is different from that of acid inorganic pyrophosphatase, which requires no metal ion for activity. The acid and alkaline inorganic pyrophosphatase activities are due to separate enzyme proteins.     

Resolution, purification and characterization of the orthophosphate releasing activities from fracture callus calcifying cartilage.

Callus calcifying cartilage alkaline phosphatase was resolved by DEAE-cellulose column chromatography into two distinct phsophatase activities. The phosphatase activity which was eluted first from the column, (phosphatase I), was active towards a variety of phosphate esters, sodium pyrophosphatase and several linear polyphosphates, while the second phosphatase activity , (phosphatase II), was active toward simple phosphate esters but not towards sodium pyrophosphate and linear oligo or polyphosphates. All the phosphate esters, sodium pyrophosphate and polyphosphates at higher concentrations were inhibitory for phosphatase I. The modulating effects of magnesium, calcium, zinc and other phosphatase modulators have been investigated. Both phosphatases from callus calcifying cartilage were found to be substrates of neuraminidase with sialic acid as the product. Besides the difference in their specificity, the phosphatases were found to be immunologically different and to have different molecular weights, strong indication that they are different enzymes.     

Adenosine triphosphate hydrolysis in rat dental tissues. A histochemical study to differentiate the enzymes involved.

The purpose of this study was to try to differentiate histochemically between the various enzymes which may catalyze the hydrolysis of ATP in developing rat dental tissues. Freeze cut and freeze dried sections of molar and incisor teeth were incubated in lead capture-based media at pH 5.0, 7.2 or 9.4 with one of the following substrates: beta-glycerophosphate, AMP, ADP, ATP, AMP-PNP and tetrasodium pyrophosphate. To establish the enzymatic nature of the hydrolysis parallel sections were incubated after prior fixation in either formaldehyde or glutaraldehyde. By comparing the enzymatic stainings obtained with the various substrates and at the different pH:s, it was concluded that ATP can be visibly hydrolyzed in rat dental tissues by alkaline phosphatase (stratum intermedium, apical part of maturation ameloblasts, basal part of all ameloblasts, odontoblasts and subodontoblastic layer), specific ATPase (apical and basal parts of secretory ameloblasts) and ATP pyrophosphatase and/or adenylate cyclase (stratum intermedium, odontoblasts). Acid phosphatase, specific ADPase, 5'-nucleotidase, inorganic pyrophosphatase, 3':5'-cyclic-AMP-phosphodiesterase and adenylate kinase on the other hand, seem not to be engaged in the ATP hydrolysis to such a degree as to complicate the interpretation of the histochemical staining. The alkaline phosphatase part of the ATP hydrolysis appeared to be rather insensitive to aldehyde fixation, while the hydrolysis effected by specific ATPase and ATP pyrophosphatase and/or adenylate cyclase was extinguished after fixation with formaldehyde for 4 h or glutaraldehyde for 10 min.