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PubMed1996

Bone alkaline phosphatase isoenzyme in renal osteodystrophy.

Serum total alkaline phosphatase is the most commonly used biochemical marker of bone disease in renal patients, but alkaline phosphatase originates from different organs and sometimes lacks specificity. Bone isoenzyme measurement is considered superior to total alkaline phosphatase for the assessment of bone metabolism. We have studied the value of bone isoenzyme, determined by a new. IRMA (Tandem-R-Ostase), in haemodialysis patients with secondary hyperparathyroidism and renal osteodystrophy. Fifty-six haemodialysis patients were studied. Intact parathyroid hormone (PTH), osteocalcin, total alkaline phosphatase and bone alkaline phosphatase were determined. A transiliac bone biopsy was performed in 20 of the 56 patients after double tetracycline labelling. There was a significant correlation between bone alkaline phosphatase and PTH (r = 0.79, P < 0.001) and between bone and total alkaline phosphatase (r = 0.84, P < 0.001) in all patients. The patients who underwent a bone biopsy showed osteitis fibrosa in 17, mixed lesion in one, adynamic bone disease in one and normal bone in one. Bone alkaline phosphatase showed a significant correlation with static and dynamic histomorphometric indices similar to that obtained with PTH and better than those of total alkaline phosphatase and osteocalcin. It is concluded that bone alkaline phosphatase (ostase) seems to be a useful non-invasive marker of bone metabolism in patients on haemodialysis with high turnover bone disease. More studies are necessary to know its value in low turnover bone disease.

Adult↗
PubMed1991

A salt-activated inositol 1,3,4,5-tetrakisphosphate 3-phosphatase at the inner surface of the human erythrocyte membrane.

The localization of the human erythrocyte membrane Ins(1,3,4,5)P4 3-phosphatase was investigated by saponin permeabilization of resealed 'isoionic' erythrocyte ghosts. This enzyme is active at the inner face of the plasma membrane, at the same site as a specific 5-phosphatase that degrades both Ins (1,4,5)P3 and Ins(1,3,4,5)P4. In the presence of EDTA, Ins(1,4,5)P3 was the only product of Ins(1,3,4,5)P4 metabolism. However, when Mg2+ was present both the 5-phosphatase and the 3-phosphatase attacked Ins (1,3,4,5)P4, directly forming Ins(1,3,4)P3 and Ins(1,4,5)P3;some Ins(1,4)P2 was also formed as a product of 5-phosphatase attack on the liberated Ins(1,4,5)P3. The Ins(1,3,4,5)P4 3-phosphatase was potently activated by KCl, thus making the route of metabolism of Ins(1,3,4,5)P4 by erythrocyte ghosts strikingly sensitive to variations in ionic strength: at 'cytosolic' K+ and Mg2+ levels, 3-phosphatase activity slightly predominated over 5-phosphatase. Ins(1,3,4,5)P4 3-phosphatase was potently inhibited by Ins-(1,3,4,5,6)P5 and InsP6 at levels lower than those often observed within cells. This leaves open the question as to whether the cellular function of inositol polyphosphate 3-phosphatase is to participate in a physiological cycle that interconverts Ins(1,3,4,5)P4 and Ins(1,4,5)P3 or to metabolize other inositol polyphosphates in the cytosol compartment of cells.

Erythrocyte Membrane↗
PubMed1990

Mechanism of glucocorticoid regulation of alkaline phosphatase gene expression in osteoblast-like cells.

In the rat osteosarcoma cell line ROS 17/2.8, glucocorticoids increase the activity of the plasma membrane enzyme, alkaline phosphatase. To determine the mechanisms responsible for this effect, we have studied the actions of dexamethasone on alkaline phosphatase activity, immunoreactive protein, and steady-state mRNA levels. Dexamethasone treatment increased both specific activity of alkaline phosphatase and the cell surface expression of immunoreactive protein in a dose-dependent manner, with a half-maximal increase at 2 nM. Steady-state alkaline phosphatase mRNA levels were also increased in a dose-dependent manner. The time course of dexamethasone induction occurred relatively slowly, with a lag period of 12 h before any discernable effect on alkaline phosphatase mRNA levels. The rise in alkaline phosphatase mRNA levels was attributable entirely to changes in gene transcription, with no effect on message stability. Treatment of ROS 17/2.8 cells with actinomycin D completely abolished the dexamethasone-induced rise in alkaline phosphatase mRNA levels. Measurement of alkaline phosphatase mRNA degradation, by incubation of cells with the transcriptional inhibitor 5,6-dichloro-ribofuranosylbenzimidazole, indicated an apparent half-life of 24 h in both untreated and dexamethasone-stimulated cells. The protein synthesis inhibitors cycloheximide and puromycin blocked the dexamethasone induction of alkaline phosphatase mRNA. These data suggest that the dexamethasone-induced rise in alkaline phosphatase gene transcription requires the synthesis of an unknown mediator protein.

Alkaline Phosphatase↗
PubMed1995

Tissue distribution and intracellular localisation of the 75-kDa inositol polyphosphate 5-phosphatase.

The 75-kDa inositol polyphosphate 5-phosphatase (75-kDa 5-phosphatase) hydrolyses several important mediators of intracellular calcium homeostasis, including inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. Northern analysis of various human tissues revealed the 75-kDa 5-phosphatase has a ubiquitous expression, where differential splicing may occur in specific tissues. Prominent expression of a 4.4-kb transcript was noted in human lung, thymus, testes and placenta, and a 4.6-kb transcript was observed in heart, brain, kidney, ovary and colon. Determination of the intracellular location of the enzyme by indirect immunofluorescence, demonstrated that the 75-kDa 5-phosphatase was associated with mitochondrial and cytosolic cellular compartments. Immunoprecipitation of the total cell homogenate of human lung carcinoma cells (A549) with anti-(recombinant 75-kDa 5-phosphatase) antibodies revealed that the 75-kDa 5-phosphatase is the major PtdIns(4,5)P2 5-phosphatase in this cell line. Analysis of PtdIns(4,5)P2 5-phosphatase activity in subcellular fractions of A549 cells revealed peak 75-kDa 5-phosphatase enzyme activity in the cytosolic and mitochondrial enriched fractions. Immunoblot analysis further confirmed the mitochondrial location of the enzyme. This study demonstrates the tissue distribution and intracellular location of the 75-kDa 5-phosphatase and reveals a novel location for an enzyme involved in phosphatidylinositol turnover.

Cell Line↗
PubMed1985

Streptococcal phosphoenolpyruvate: sugar phosphotransferase system: purification and characterization of a phosphoprotein phosphatase which hydrolyzes the phosphoryl bond in seryl-phosphorylated histidine-containing protein.

Histidine-containing protein (HPr) of gram-positive bacteria was found to be phosphorylated at a seryl residue (P-ser-HPr) in an ATP-dependent reaction catalyzed by a protein kinase (J. Deutscher and M. H. Saier, Jr., Proc. Natl. Acad. Sci. U.S.A. 80:6790-6794, 1983). Here we describe the purification and characterization of a soluble enzyme of Streptococcus faecalis which splits the phosphoryl bond in P-ser-HPr. The enzyme has a molecular weight of ca. 7.5 X 10(4), as determined by its migration behavior on a Sephacryl S-200 column. On native polyacrylamide gels the purified enzyme produced only one protein band. On sodium dodecyl sulfate-polyacrylamide gels we found one major protein band of molecular weight 2.9 X 10(4) and two minor protein bands of molecular weights 2.3 X 10(4) and 7 X 10(4). Fructose 1,6-diphosphate, which stimulated the ATP-dependent, protein kinase-catalyzed phosphorylation of HPr, had no effect on the phosphatase activity. Other glycolytic intermediates also had no effect. However, inorganic phosphate, which inhibited the ATP-dependent HPr kinase, stimulated the P-ser-HPr phosphatase. EDTA at a concentration of 0.1 mM completely inhibited the phosphatase. Divalent cations like Mg2+, Mn2+, and Co2+ overcame the inhibition by EDTA. Fe2+, Zn2+, and Cu2+ had no effect, whereas Ca2+ slightly inhibited the phosphatase. ATP was also found to inhibit the phosphatase. Under conditions in which ATP severely inhibited the phosphatase, ADP was found to have no effect on the enzyme activity. Besides P-ser-HPr of S. faecalis, the phosphatase was also able to hydrolyze the phosphoryl bond in P-ser-HPr of Streptococcus lactis, Staphylococcus aureus, Bacillus subtilis, Streptococcus pyogenes, and Lactobacillus casei. Phosphoenolpyruvate-dependent o-nitrophenyl-beta-D-galactopyranoside phosphorylation, catalyzed by the S. aureus phosphoenolpyruvate:lactose phosphotransferase system, was about 150-fold decreased in the presence of P-ser-HPr of S. aureus, as compared with HPr. However, when P-ser-HPr was first incubated with P-ser-HPr phosphatase to allow complete hydrolysis of the phosphoryl bond, it had the same activity as HPr. Besides this cytoplasmic phosphoprotein phosphatase, we detected a membrane-bound phosphatase which also hydrolyzed the phosphoryl bond in P-ser-HPr.

Bacterial Proteins↗
PubMed1991

Isolation, transcription, and inactivation of the gene for an atypical alkaline phosphatase of Synechococcus sp. strain PCC 7942.

The alkaline phosphatase of Synechococcus sp. strain PCC 7942 is 145 kDa, which is larger than any alkaline phosphatase previously characterized and approximately three times the size of the analogous enzyme in Escherichia coli. The gene for the alkaline phosphatase, phoA, was cloned and sequenced, and the protein that it encodes was found to have little similarity to other phosphatases. Some sequence similarities were observed between the Synechococcus sp. strain PCC 7942 alkaline phosphatase, the alpha subunit of the ATPase from bacteria and chloroplasts, and the UshA sugar hydrolase of E. coli. Also, limited sequence similarity was observed between a region of the phosphatase and a motif implicated in nucleotide binding. Interestingly, although the alkaline phosphatase is transported across the inner cytoplasmic membrane and into the periplasmic space, it does not appear to have a cleavable signal sequence at its amino terminus. The half-life of the mRNA encoding the alkaline phosphatase, measured after inhibition of RNA synthesis, is approximately 5 min. Similar kinetics for the loss of alkaline phosphatase mRNA occur upon the addition of phosphate to phosphate-depleted cultures, suggesting that high levels of this nutrient inhibit transcription from phoA almost immediately. The phoA gene also appears to be the first gene of an operon; the largest detectable transcript that hybridizes to a phoA gene-specific probe is 11 kb, over twice the size needed to encode the mature protein. Other phosphate-regulated mRNAs are also transcribed upstream of the phoA gene. Insertional inactivation of phoA results in the loss of extracellular, phosphate-regulated phosphatase activity but does not alter the capacity of the cell for phosphate uptake.

Alkaline Phosphatase↗
PubMed1985

Resistance of leishmanial phosphatases to inactivation by oxygen metabolites.

Leishmania donovani promastigotes produce large quantities of two distinct acid phosphatases; a tartrate-resistant enzyme is localized to the external surface of the plasma membrane, and a tartrate-sensitive enzyme is secreted into the growth medium. It was shown previously that preincubation of human neutrophils and macrophages with the tartrate-resistant phosphatase markedly reduced the ability of these host cells to produce superoxide anions in response to stimulation with the activator formyl-methionyl-leucyl-phenylalanine. The possibility that the cell surface acid phosphatase or the phosphatase that is secreted into the extracellular fluid might compromise other host cell functions, especially intracellular ones, depends on the ability of the enzyme to resist exposure to toxic oxygen metabolites (e.g., superoxide anion, hydrogen peroxide, hypochlorite) generated by phagocytic cells. In the present report, we show that both leishmanial acid phosphatases were relatively resistant to inactivation by oxygen metabolites. At pH 5.5, the activity of the tartrate-resistant phosphatase was reduced 50% by incubation for 1 h with each of the following: 30 mM O2-, 500 mM hydrogen peroxide, and 6 mM hypochlorite ion. These concentrations are many fold greater than the concentrations of these substances that are generated by stimulated polymorphonuclear phagocytes. The tartrate-sensitive acid phosphatase differed markedly from the tartrate-resistant phosphatase in that the former was essentially insensitive to even very high concentrations of superoxide anion and hydrogen peroxide. Furthermore, 50% inactivation of the tartrate-sensitive leishmanial phosphatase required exposure to 35 mM hypochlorite for 30 min. These results indicate that the catalytic potential of these two leishmanial acid phosphatases probably survives exposure to toxic oxygen metabolites generated by neutrophils and macrophages.

Acid Phosphatase↗
PubMed2000

Role of protein phosphatases in the activation of CFTR (ABCC7) by genistein and bromotetramisole.

Genistein and bromotetramisole (Br-t) strongly activate cystic fibrosis transmembrane conductance regulator (CFTR; ABCC7) chloride channels on Chinese hamster ovary cells and human airway epithelial cells. We have examined the possible role of phosphatases in stimulation by these drugs using patch-clamp and biochemical methods. Genistein inhibited the spontaneous rundown of channel activity that occurs after membrane patches are excised from cAMP-stimulated cells but had no effect on purified protein phosphatase type 1 (PP1), PP2A, PP2B, PP2C, or endogenous phosphatases when assayed as [(32)P]PO(4) release from prelabeled casein, recombinant GST-R domain fusion protein, or immunoprecipitated full-length CFTR. Br-t also slowed rundown of CFTR channels, but, in marked contrast to genistein, it did inhibit all four protein phosphatases tested. Half-maximal inhibition of PP2A and PP2C was observed with 0.5 and 1.5 mM Br-t, respectively. Protein phosphatases were also sensitive to (+)-p-Br-t, a stereoisomer of Br-t that does not inhibit alkaline phosphatases. Br-t appeared to act exclusively through phosphatases since it did not affect CFTR channels in patches that had low apparent endogenous phosphatase activity (i.e., those lacking spontaneous rundown). We conclude that genistein and Br-t act through different mechanisms. Genistein stimulates CFTR without inhibiting phosphatases, whereas Br-t acts by inhibiting a membrane-associated protein phosphatase (probably PP2C) that presumably allows basal phosphorylation to accumulate.

Animals↗
PubMed1982

Inactivation and reactivation of rat liver 3-hydroxy-3-methylglutaryl-CoA-reductase phosphatases: effect of phosphate, pyrophosphate and divalent cations.

Incubation of four purified rat liver HMG-CoA-reductase phosphatases (Gil, G., Sitges, M. and Hegardt, F.G. (1981) Biochim. Biophys. Acta 663, 211-221) with Mn2 or Mg2 caused a concentration-dependent activation of enzyme activities. The maximum effect for Mn2 was at 5 mM for all phosphatases. Fe2 caused inactivation only in reductase phosphatases IIa and IIb. Ca2 10 mM showed a slight effect of inactivation. Phosphate, pyrophosphate and adenine nucleotides inhibited the four reductase phosphatases, this process being concentration-dependent. cAMP did not inhibit the four phosphatases at all in the range of 0.01-8 mM. Preincubation of reductase phosphatases with PPi and subsequent dilution did not diminish the inactivation effect, showing that this ion inhibits the enzyme prior to the binding to the substrate. Phosphorylated sugars, but not free sugar, inactivated the four reductase phosphatases. PPi-inactivated enzymes were reactivated by Mg2 or Mn2, this process being time-dependent. The four phosphatases had different patterns of reactivation. Phosphatases Ib and IIb (low-molecular mass forms) were shown to be different enzymes as judged by: their divergent behaviour when inhibited with Fe2; their PPi response; kinetics of reactivation by Mg2 or Mn2 or PPi-inactivated enzymes; and thermal stability. A metalloenzyme character is suggested for reductase phosphatases.

Adenine Nucleotides↗
PubMed1988

Alkaline phosphatase isozymes in non-malignant intestinal and hepatic diseases.

Human alkaline phosphatase isozymes--the tissue-unspecific, the intestinal, and the placental alkaline phosphatases--were determined in sera by use of isozyme-specific monoclonal antibodies. The clinical utility of serum determinations of alkaline phosphatase isozymes was evaluated in patients with diseases of the gastrointestinal tract and the liver. No elevations of the different serum isozymes were observed in the intestinal diseases investigated (active Crohn's disease and ulcerative colitis). For non-malignant diseases of the liver the alkaline phosphatase isozymes presented characteristic patterns. Patients with cirrhosis due to hepatocellular diseases had markedly elevated levels of intestinal alkaline phosphatase and moderate serum activities of tissue-unspecific and placental alkaline phosphatases. In patients with liver disease with cholestatic features tissue-unspecific and placental isozyme levels were high, but the intestinal isozyme remained normal, whereas primary biliary cirrhosis was associated with high levels of the tissue-unspecific enzyme and moderate elevations of intestinal and placental alkaline phosphatases. It can be concluded that, in addition to tissue-unspecific alkaline phosphatase, intestinal and placental isozymes contribute to the total alkaline phosphatase activity for patients with liver disease. The results suggest that specific methods for the identification of alkaline phosphatase isozymes could be of value.

Alkaline Phosphatase↗
PubMed1996

Utilization of the bone/liver alkaline phosphatase activity ratio in blood plasma as an indicator of ascorbate deficiency in salmonid fish.

The goal of this study was to test the hypothesis that the ratio of liver to bone alkaline phosphatase in blood plasma reflects the ascorbate status in scurvy-prone teleost fish (rainbow trout [Oncorhynchus mykiss]). The studies focused on finding a method for distinguishing bone alkaline phosphatase present in blood plasma from other alkaline phosphatase isoforms. We tested temperature optima and thermostability of liver, kidney, gill cartilage, and intestinal alkaline phosphatases. We did not observe differences among liver, bone, and kidney enzymes with respect to temperature optima and thermostability. We partially purified alkaline phosphatase from juvenile rainbow trout vertebrae and liver using n-butanol solubilization and ammonium sulfate fractionation. We found a difference between bone alkaline phosphatase, which precipitated in 0%-20% ammonium sulfate saturation, and liver enzyme, which required 40%-50% ammonium sulfate saturation to precipitation. We conducted a series of urea inactivation studies on partially purified enzymes from liver and vertebrae. Urea differentially inhibited the enzymes with t 1/2 = 1.1 and 0.4 min, for bone and liver, respectively. Subsequently, we subjected blood plasma alkaline phosphatase to urea inhibition, and using regression analysis we calculated the ratio of liver to bone alkaline phosphatase. We found that thus obtained ratios of bone enzyme in blood plasma correlated with liver ascorbate concentration. Bone alkaline phosphatase declined in ascorbate deficiency 10-fold, whereas low ascorbate status resulted in a 3.5-fold decrease. In order to draw a general conclusion on the linearity of the response of blood plasma/bone alkaline phosphatase as an indicator of ascorbate deficiency in fish, further studies must include analysis of individual fish followed in the process of developing avitaminosis.

Alkaline Phosphatase↗
PubMed2004

Assessment of pasteurisation of milk and cream produced by on-farm dairies using a fluorimetric method for alkaline phosphatase activity.

The alkaline phosphatase test is used as an indicator of adequate pasteurisation of milk and cream. A proprietary fluorimetric technique (Fluorophos) is a sensitive and quantitative method for the determination of alkaline phosphatase (ALP) activity in milk products. Currently, adequate pasteurisation of milk products is regarded as confirmed in samples that contain a residual bovine ALP activity of < or =500 mU/litre. This is equivalent to the statutory acceptable level of 4ug phenol/ml required by the EC analytical method. The purpose of the present study was to assess the effectiveness of pasteurisation of milk and cream produced by on-farm dairies. In a longitudinal study over a four-year period, 4,999 samples of milk and cream were collected from 130 on-farm dairies and from two large commercial dairies in NW England for comparison. Bovine ALP activity of >500 mU/litre was deemed as a failure and was found in 3.5% of whole milk, 2.4% semiskimmed milk, 5.0% of skimmed milk, and 39% of cream samples from on-farm dairies. Bovine ALP activity of >100 and <500 mU/litre was found in 18.4% of whole milk, 9.3% of semi-skimmed milk, 13.2% skimmed milk and 44.5% of cream samples from on-farm dairies. Results with skimmed milk samples showed significantly lower bovine ALP activity than whole milk. All 409 milk and cream samples from two large commercial dairies passed the fluorimetric test at less than 500 mU/litre of bovine ALP, and 99% of these milk and cream samples had bovine ALP activity of less than 100 mU/litre. The presence of residual bovine phosphatase indicates a failure and may be due to either inadequate pasteurisation or post pasteurisation contamination with raw milk. Residual bovine phosphatase was demonstrated in 108/114 (94.7%) of milk samples with a bovine ALP activity greater than 500 mU/litre, i.e. true failures. Of more concern is that residual bovine phosphatase was found in 395/401 (98.5%) of samples that gave bovine ALP activity greater than 100 mU/litre but equal to or less than 500 mU/litre. Residual bovine phosphatase was demonstrated in 37/108 (30.2%) of cream samples with bovine ALP activity greater than 500 mU/litre. Presence of reactivated bovine phosphatase is not an indication of a failure but can mask the presence of residual bovine phosphatase. Reactivated bovine phosphatase was found in 74/106 (69.8%) of cream samples. Our results confirm that the more sensitive fluorimetric method is suitable for testing pasteurised whole milk and semiskimmed milk, but for statutory purposes the acceptable level of residual bovine phosphatase should be <100 mU/litre. Our findings have highlighted a potential problem when testing skimmed milk and cream samples from on-farm dairies. To ensure public safety we need more stringent standards for the ALP test and new methods that will accurately confirm that pasteurisation of these products has been achieved.

Alkaline Phosphatase↗
PubMed2004

Characterization of protein tyrosine phosphatase activity in rat liver microsomes: suppressive effect of endogenous regucalcin in transgenic rats.

The role of regucalcin, a regulatory protein in intracellular signaling system, in the regulation of protein phosphatase activity in rat liver microsomes was investigated. Protein phosphatase activity torward phosphotyrosine, phosphoserine, and phosphothreonine was assayed in a reaction mixture containing the microsomal protein. Protein phosphatase activity toward phosphotyrosine was strong as compared with that of the enzyme activity toward phosphoserine and phosphothreonine, indicating the existence of protein tyrosine phosphatase. Protein phosphatase activity toward three phosphoaminoacids was significantly enhanced by the addition of both calcium chloride (10 micro M) and calmodulin (2.5 or 5 micro g/ml) in the reaction mixture. The presence of ethylene glycol bis (2-amino-ethylether) N, N, N', N'-tetracetic acid (EGTA; 0.1, 1 or 2 mM) or trifluoperazine (TFP; 10, 20 or 50 micro M), an antagonist of calmodulin, did not have a significant effect on protein phosphatase activity toward phosphotyrosine without calcium addition. Microsomal protein tyrosine phosphatase activity was not changed by okadaic acid (10(-6)-10(-4) M). The enzyme activity was significantly decreased by vanadate (10, 50 or 100 micro M). The addition of regucalcin (0.25 or 0.5 micro M) in the reaction mixture caused a significant inhibition of protein tyrosine phosphatase activity in liver microsomes. Western blot analysis showed a remarkable increase in regucalcin protein level in the liver microsomes of regucalcin transgenic (TG) rats. Protein tyrosine phosphatase activity was significantly suppressed in the liver microsomes of TG rats. This study demonstrates that protein tyrosine phosphatase activity is found in the liver microsomes, and that the enzyme activity is suppressed by regucalcin.

Animals↗
PubMed1989

Processing, transport, and secretion of the lysosomal enzyme acid phosphatase in Dictyostelium discoideum.

To explain the different secretion kinetics of lysosomal enzymes in Dictyostelium discoideum, previous investigators have hypothesized the existence of a heterogeneous population of lysosomes containing either the enzyme acid phosphatase or other hydrolase enzymes. This proposal predicts that at least two targeting mechanisms exist for lysosomal enzymes in this organism. To begin to investigate this possibility, the transport, processing, and targeting of acid phosphatase was studied by using a combination of radiolabel pulse-chase procedures, subcellular fractionations, and indirect immunofluorescence microscopy. Acid phosphatase was initially synthesized in axenically growing cells as a 56-kDa precursor polypeptide that was proteolytically processed after 20 min to a 55-kDa mature protein. This enzyme was rapidly transported from the endoplasmic reticulum to Golgi complex (halftime of 3 min) as measured by the acquisition of resistance to the enzyme endoglycosidase H. Furthermore, Percoll gradient fractionations indicated that radiolabeled forms of acid phosphatase reached dense lysosomal vesicles at about the same time as final processing was occurring. Proper sorting of acid phosphatase in D. discoideum apparently was not critically dependent on low intravacuolar pH since the addition of ammonium chloride did not stimulate the missorting and secretion of acid phosphatase. These results are very similar to previous observations concerning other Dictyostelium lysosomal enzymes. Consistent with the existence of a heterogeneus population of lysosomes, the percentage of radiolabeled acid phosphatase secreted 4 h into a chase period was 15-fold lower as compared with another lysosomal enzyme, beta-glucosidase. However, acid phosphatase, alpha-mannosidase, and beta-glucosidase were all predominantly colocalized as determined by indirect immunofluorescence, which for the first time demonstrates the homogeneous nature of the lysosomal system in D. discoideum. Taken together these results suggest that the processing and transport of acid phosphatase may be similar in nature to the glycosidases. However, the different kinetics of secretion of acid phosphatase versus the colocalized glycosidase enzymes suggests that an undefined mechanism operates to distinguish these classes of enzymes at a step after localization to lysosomes but prior to secretion.

Acid Phosphatase↗
PubMed1988

PHO5-LACZ hybrid proteins block translocation of native acid phosphatase in Saccharomyces cerevisiae.

A set of protein hybrids composed of variable portions of the amino-terminal residues of the yeast phosphate-repressible acid phosphatase (product of PHO5) and an active fragment of bacterial beta-galactosidase has been constructed. When these PHO5-LACZ hybrids are expressed in a yeast strain carrying an intact chromosomal PHO5 gene, they show a size-dependent interference with the secretion of native acid phosphatase. Hybrid proteins containing approximately 50 residues of acid phosphatase do not affect secretion of native acid phosphatase. Hybrids containing greater than 200 residues of acid phosphatase reduce the amount of secreted acid phosphatase more than by 50%. The interference with secretion is specific for acid phosphatase. The hybrids do not affect secretion of invertase, and do not confer a growth-deficient phenotype on yeast. Both the hybrid proteins and acid phosphatase accumulate in non-glycosylated, membrane-bound forms which are sensitive to proteolysis from the cytoplasmic side of the membrane. The hybrids and accumulated acid phosphatase co-migrate on Percoll density gradients with markers of the endoplasmic reticulum, but not with markers of the Golgi or secretory vesicles. These results suggest that PHO5-LACZ hybrid proteins specifically block secretion of native acid phosphatase by interfering with enzyme after targeting but before translocation across the endoplasmic reticulum.

Acid Phosphatase↗
PubMed1977

Purification and properties of two acid phosphatases from midgut glands of abalone Haliotis discus.

Midgut glands of abalone Haliotis discus contained two acid phosphatases [orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2] separable by phosphocellulose column chromatography. They were designated as acid phosphatases I and II in order of elution and were purified 99- and 290-fold, respectively. Purified acid phosphatase II was nearly homogeneous as judged by polyacrylamide gel electrophoresis. The substrate specificity of acid phosphatase I was narrow, whereas that of acid phosphatase II was broad. Good substrates for acid phosphatase I included p-nitrophenyl phosphate, phosphoenolpyruvate, inorganic pyrophosphate, and nucleoside di- and triphosphates. The acid phosphatases did not require any metal ion for maximum activity and were inhibited by Zn2+, Cu2+ and Hg2+. Fluoride and arsenate were potent inhibitors of both enzymes. The pH optima of acid phosphatases I and II were 5.9 and 5.5, respectively. The molecular weights of acid phosphatases I and II were estimated to be 28,000 and 100,000, respectively, by gel filtration on Sephadex G-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggested that acid phosphatase II consists of two identical subunits.

Acid Phosphatase↗
PubMed1976

Evidence for the coordinate control of activity of liver glycogen synthase and phosphorylase by a single protein phosphatase.

Homogeneous rabbit liver phosphorylase phosphatase (Brandt, H., Capulong, Z. L., and Lee, E. Y. C. (1975) J. Biol. Chem. 250, 8038-8044) also dephosphorylates glycogen synthase b. During purification, phosphorylase phosphatase and glycogen synthase phosphatase co-purified with a constant ratio of activities. The two activities co-migrated on disc gel electrophoresis. Both substrates competed with each other for the phosphatase, and both phosphatase activities were inhibited by lysine ethyl ester. It is concluded that liver phosphorylase phosphatase and glycogen synthase phosphatase have a common identity and that coordinate regulation of the phosphatase-catalyzed activation of glycogen synthase and inactivation of phosphorylase occurs in vivo. This provides a parallel and opposing mechanism to that mediated by adenosine 3':5'-monophosphate-dependent protein kinase, which coordinately inactivates glycogen synthase and, via phosphorylase kinase, activates phosphorylase. Maximal glycogen synthase phosphatase activity was observed near neutrality. Mg2+ and glucose-6-P activated the glycogen synthase phosphatase reaction and this activation was pH-dependent. The Km for glycogen synthase b was 0.12 muM.

Animals↗
PubMedDate not supplied

Induction of rat liver alkaline phosphatase by bile duct ligation.

Bile duct ligation causes a five- to sevenfold increase in the activity of rat liver alkaline phosphatase within 12 hours after ligation and a similar rise in the activity of alkaline phosphatase in serum. The increased serum activity is due entirely to the appearance of a new isoenzyme that has the properties of rat liver alkaline phosphatase. The increase in both serum and liver alkaline phosphatase is prevented by the prior administration of cycloheximide in a dose that inhibits protein synthesis by 70%. Rat liver alkaline phosphatase was then purified to homogeneity. Antibody was raised to purified rat liver alkaline phosphatase in rabbits. The antibody was coupled to sepharose 4B and affinity columns made. (3)-H-leucine was then injected into the portal veins of sham operated rats and rats with bile duct ligation four hours after ligation. One hour after injection and five hours after ligation, animals were sacrificed. Liver alkaline phosphatase was purified by means of affinity chromatography and double immunoprecipitation with rabbit antibody to rat liver alkaline phosphatase and goat anti-rabbit gamma globulin. Bile duct ligation increased the incorporation of (3)-H-leucine into liver alkaline phosphatase more than threefold compared with sham operated rats, 164 CPM/mg protein vs. 49 CPM/mg protein (p < .001). The data indicate that the increased activity of rat liver alkaline phosphatase after bile duct ligation is due to enzyme induction rather than to activation of a pre-existing, relatively inactive enzyme.

Alkaline Phosphatase↗