Alkaline phosphatase

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Alkaline phosphatase
1ALK.png
Ribbon diagram (rainbow-color, N-terminus = blue, C-terminus = red) of the dimeric structure of bacterial alkaline phosphatase.[1]
Identifiers
EC number 3.1.3.1
CAS number 9001-78-9
Databases
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO
Alkaline phosphatase
PDB 1alk EBI.jpg
Structure of alkaline phosphatase.[1]
Identifiers
Symbol Alk_phosphatase
Pfam PF00245
InterPro IPR001952
SMART SM00098
PROSITE PDOC00113
SCOP 1alk
SUPERFAMILY 1alk

Alkaline phosphatase (ALP, ALKP, ALPase, Alk Phos) (EC 3.1.3.1) is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation. As the name suggests, alkaline phosphatases are most effective in an alkaline environment; it is sometimes used synonymously as basic phosphatase.[2] Undifferentiated pluripotent stem cells have elevated levels of alkaline phosphatase on their cell membrane.[3]

Bacterial[edit]

In Gram-negative bacteria, alkaline phosphatase is located in the periplasmic space, external to the cell membrane. Since this space is much more subject to environmental variation than the actual interior of the cell, bacterial alkaline phosphatase is resistant to inactivation, denaturation, and degradation, and contains a higher rate of activity. Although the purpose of the enzyme is not fully resolved, the simple hypothesis is that it serves to cleave phosphate groups from phosphorylated compounds facilitating transport across membranes and providing the cell with a source of inorganic phosphate at times of phosphate starvation.The main purpose of dephosphorylation by alkaline phosphatase is to increase the rate of diffusion of the molecules into the cells and inhibit them from diffusing out.[4] However, other possibilities exist. For instance, the presence of phosphate groups usually prevents organic molecules from passing through the membrane; therefore, dephosphorylating them may be important for bacterial uptake of organic compounds.

Alkaline phosphatase is a zinc-containing dimeric enzyme with the MW: 86,000 kDa. It is heat stable and its function is to remove phosphate groups from phosphorylated compounds facilitating transport across membranes and providing the cell with a source of inorganic phosphate. Alkaline phosphatase in E. coli is located in the periplasmic space and can thus be released using techniques that weaken the cell wall and release the protein. Due to the location of the enzyme, and the protein layout of the enzyme the enzyme is in solution with a small amount of proteins than there are in another portion of the cell. [5] Some complexities of bacterial regulation and metabolism suggest that other, more subtle, purposes for the enzyme may also play a role for the cell. In the laboratory, however, mutant Escherichia coli lacking alkaline phosphatase survive quite well, as do mutants unable to shut off alkaline phosphatase production.[6]

The optimal pH for the activity of the E. coli enzyme is 8.0[7] while the bovine enzyme optimum pH is slightly higher at 8.5.[8]

Use in research[edit]

By changing the amino acids of the wild-type alkaline phosphatase enzyme produced by Escherichia coli, a mutant alkaline phosphatase is created which not only has a 36-fold increase in enzyme activity, but also retains thermal stability.[9] Typical uses in the lab for alkaline phosphatases include removing phosphate monoesters to prevent self-ligation, which is undesirable during plasmid DNA cloning.[10]

Common alkaline phosphatases used in research include:

  • Shrimp alkaline phosphatase (SAP), from a species of Arctic shrimp (Pandalus borealis). This phosphatase is easily inactivated by heat, a useful feature in some applications.
  • Calf-intestinal alkaline phosphatase (CIP)
  • Placental alkaline phosphatase (PLAP) and its C terminally truncated version that lacks the last 24 amino acids (constituting the domain that targets for GPI membrane anchoring) - the secreted alkaline phosphatase (SEAP). It presents certain characteristics like heat stability, substrate specificity, and resistance to chemical inactivation.[11]
  • Human-intestinal alkaline phosphatase. The human body has multiple types of alkaline phosphatase present, which are determined by a minimum of three gene loci. Each one of these three loci controls a different kind of alkaline phosphatase isozyme. However, the development of this enzyme can be strictly regulated by other factors such as thermostability, electrophoresis, inhibition, or immunology.[12]

Human-intestinal ALPase shows around 80% homology with bovine intestinal ALPase, which holds true their shared evolutionary origins. That same bovine enzyme has more than 70% homology with human placental enzyme. However, the human intestinal enzyme and the placental enzyme only share 20% homology despite their structural similarities.[13]

Alkaline phosphatase has become a useful tool in molecular biology laboratories, since DNA normally possesses phosphate groups on the 5' end. Removing these phosphates prevents the DNA from ligating (the 5' end attaching to the 3' end), thereby keeping DNA molecules linear until the next step of the process for which they are being prepared; also, removal of the phosphate groups allows radiolabeling (replacement by radioactive phosphate groups) in order to measure the presence of the labeled DNA through further steps in the process or experiment. For these purposes, the alkaline phosphatase from shrimp is the most useful, as it is the easiest to inactivate once it has done its job.

Another important use of alkaline phosphatase is as a label for enzyme immunoassays.

Because undifferentiated pluripotent stem cells have elevated levels of alkaline phosphatase on their cell membrane, therefore alkaline phosphatase staining is used to detect these cells and to test pluripotency (i.e., embryonic stem cells or embryonal carcinoma cells).[3]

Ongoing research[edit]

Current researchers are looking into the increase of tumor necrosis factor-α and its direct effect on the expression of alkaline phosphatase in vascular smooth muscle cells as well as how alkaline phosphatase (AP) affects the inflammatory responses and may play a direct role in preventing organ damage.[14]

  • Alkaline phosphatase (AP) affect on the inflammatory responses in patients with Chronic kidney disease and is directly associated with Erythropoiesis stimulating agent resistant anemia.[15]
  • Intestinal alkaline phosphatase (IAP) and the mechanism it uses to regulate pH and ATP hydrolysis in rat duodenum.[16]
  • Testing the effectiveness of the inhibitor and its impact on IAP in acute intestinal inflammation as well as explore the molecular mechanisms of IAP in "ameliorating intestinal permeability."[17]

Dairy industry[edit]

Alkaline phosphatase is commonly used in the dairy industry as an indicator of successful pasteurization. This is because the most heat stable bacterium found in milk, Mycobacterium paratuberculosis, is destroyed by temperatures lower than those required to denature ALP. Therefore, ALP presence is ideal for indicating successful pasteurization.[18][19]

Pasteurization verification is typically performed by measuring the fluorescence of a solution which becomes fluorescent when exposed to active ALP. Fluorimetry assays are required by milk producers in the UK to prove alkaline phosphatase has been denatured,[20] as p-Nitrophenylphosphate tests are not considered accurate enough to meet health standards.

Alternatively the colour change of a para-Nitrophenylphosphate substrate in a buffered solution (Aschaffenburg Mullen Test) can be used.[21] Raw milk would typically produce a yellow colouration within a couple of minutes, whereas properly pasteurised milk should show no change. There are exceptions to this, as in the case of heat-stable alkaline phophatases produced by some bacteria, but these bacteria should not be present in milk.

Inhibitors[edit]

All mammalian alkaline phosphatase isoenzymes except placental (PALP and SEAP) are inhibited by homoarginine, and, in similar manner, all except the intestinal and placental ones are blocked by levamisole. Heating for ~2 hours at 65 °C inactivates most isoenzymes except placental isoforms (PALP and SEAP).[22] Phosphate is another inhibitor which competitively inhibits alkaline phosphatase.[23]

Another known example of a alkaline phosphatase inhibitor is [(4-Nitrophenyl)methyl]phosphonic acid.[24]

Human[edit]

Physiology[edit]

In humans, alkaline phosphatase is present in all tissues throughout the entire body, but is particularly concentrated in the liver, bile duct, kidney, bone, intestinal mucosa and placenta. In the serum, two types of alkaline phosphatase isozymes predominate: skeletal and liver. During childhood the majority of alkaline phosphatase are of skeletal origin.[25] Humans and most other mammals contain the following alkaline phosphatase isozymes:

  • ALPI – intestinal (molecular weight of 150 kDa)
  • ALPL – tissue-nonspecific (liver/bone/kidney)
  • ALPP – placental (Regan isozyme)

Alkaline Phosphatase in cancer cells

Studies show that the alkaline phosphatase protein found in cancer cells has similar characteristics to that found in non-malignant body tissues. Results show that the protein has originated from the same gene in both the malignant and the non-malignant cells. A study conducted by scientists Patricia J. Greene and Howard H. Sussman tested the structural comparison between the alkaline phosphatase proteins found in liver giant-cell carcinoma and non-malignant placental cells. In this study, an alkaline phosphatase that was immunochemically similar to placental alkaline phosphatase was purified from metastases of giant-cell carcinoma of the lung and its physical and chemical properties were determined. Thereafter, these were compared with purified placental alkaline phosphatase. The results showed great similarity in both based on evaluations of NH2-terminal sequence, peptide map, subunit molecular weight, and isoelectronic point. Overall, this study strongly supports the supposition that the alkaline phosphatase protein in both tumor and non-malignant placental cells are derived from the same gene.[26]

In a different study in which scientists examined alkaline phosphatase protein presence in a human colon cancer cell line, also known as HT-29, results showed that the enzyme activity was similar to that of the non-malignant intestinal type. However, this study revealed that without the influence of sodium butyrate, alkaline phosphatase activity is fairly low in cancer cells.[27] A study based on sodium butyrate effects on cancer cells conveys that it has an effect on androgen receptor co-regulator expression, transcription activity, and also on histone acetylation in cancer cells.[28] This explains why the addition of sodium butyrate show increased activity of alkaline phosphatase in the cancer cells of the human colon.[27] In addition, this further supports the theory that alkaline phosphatase enzyme activity is actually present in cancer cells.

In another study, choriocarcinoma cells were grown in the presence of 5-bromo-2’-deoxyuridine (BrdUrd) and results conveyed a 30- to 40- fold increase in alkaline phosphatase activity. This procedure of enhancing the activity of the enzyme is known as enzyme induction. The evidence shows that there is in fact activity of alkaline phosphatase in tumor cells, but it is minimal and needs to be enhanced. Results from this study further indicate that activities of this enzyme vary among the different choriocarcinoma cell lines and that the activity of the alkaline phosphatase protein in these cells is lower than in the non-malignant placenta cells.[29][30] but levels are significantly higher in children and pregnant women. Blood tests should always be interpreted using the reference range from the laboratory that performed the test. High ALP levels can occur if the bile ducts are obstructed.[31] Also, ALP increases if there is active bone formation occurring, as ALP is a byproduct of osteoblast activity (such as the case in Paget's disease of bone). Levels are also elevated in people with untreated coeliac disease.[32] Lowered levels of ALP are less common than elevated levels. The source of elevated ALP levels can be deduced by obtaining serum levels of gamma glutamyltransferase (GGT). Concomitant increases of ALP with GGT should raise the suspicion of hepatobiliary disease.[33]

Some diseases do not affect the levels of alkaline phosphatase, for example, hepatitis C. A high level of this enzyme does not reflect any damage in the liver, even though high alkaline phosphatase levels may result from a blockage of flow in the biliary tract or an increase in the pressure of the liver.[34]

Elevated levels[edit]

If it is unclear why alkaline phosphatase is elevated, isoenzyme studies using electrophoresis can confirm the source of the ALP. Skelphosphatase (which is localized in osteoblasts and extracellular layers of newly synthesized matrix) is released into circulation by a yet unclear mechanism.[35] Placental alkaline phosphatase is elevated in seminomas[36] and active forms of rickets, as well as in the following diseases and conditions:[37]

Lowered levels[edit]

The following conditions or diseases may lead to reduced levels of alkaline phosphatase:

In addition, the following drugs have been demonstrated to reduce alkaline phosphatase:

  • Oral contraceptives[39]

Prognostic Uses[edit]

Measuring alkaline phosphatase (along with prostate specific antigen) during, and after six months of hormone treated metastatic prostate cancer was shown to predict the survival of patients.[40]

Leukocyte alkaline phosphatase[edit]

Leukocyte alkaline phosphatase (LAP) is found within mature white blood cells. White blood cell levels of LAP can help in the diagnosis of certain conditions.

See also[edit]

References[edit]

  1. ^ a b PDB: 1ALK​: Kim EE, Wyckoff HW (March 1991). "Reaction mechanism of alkaline phosphatase based on crystal structures. Two-metal ion catalysis". J. Mol. Biol. 218 (2): 449–64. doi:10.1016/0022-2836(91)90724-K. PMID 2010919. 
  2. ^ Tamás L, Huttová J, Mistrk I, Kogan G (2002). "Effect of Carboxymethyl Chitin-Glucan on the Activity of Some Hydrolytic Enzymes in Maize Plants" (PDF). Chem. Pap. 56 (5): 326–329. 
  3. ^ a b "Appendix E: Stem Cell Markers". Stem Cell Information. National Institutes of Health, U.S. Department of Health and Human Services. Retrieved 2013-09-24. 
  4. ^ Horiuchi T, Horiuchi S, Mizuno D (May 1959). "A possible negative feedback phenomenon controlling formation of alkaline phosphomonoesterase in Escherichia coli". Nature. 183 (4674): 1529–30. doi:10.1038/1831529b0. PMID 13666805. 
  5. ^ Ammerman JW, Azam F (March 1985). "Bacterial 5-nucleotidase in aquatic ecosystems: a novel mechanism of phosphorus regeneration". Science. 227 (4692): 1338–40. doi:10.1126/science.227.4692.1338. PMID 17793769. 
  6. ^ Wanner BL, Latterell P (October 1980). "Mutants affected in alkaline phosphatase, expression: evidence for multiple positive regulators of the phosphate regulon in Escherichia coli". Genetics. 96 (2): 353–66. PMC 1214304Freely accessible. PMID 7021308. 
  7. ^ Garen A, Levinthal C (March 1960). "A fine-structure genetic and chemical study of the enzyme alkaline phosphatase of E. coli. I. Purification and characterization of alkaline phosphatase". Biochim. Biophys. Acta. 38: 470–83. doi:10.1016/0006-3002(60)91282-8. PMID 13826559. 
  8. ^ Harada M, Udagawa N, Fukasawa K, Hiraoka BY, Mogi M (February 1986). "Inorganic pyrophosphatase activity of purified bovine pulp alkaline phosphatase at physiological pH". J. Dent. Res. 65 (2): 125–7. doi:10.1177/00220345860650020601. PMID 3003174. 
  9. ^ W, MANDECKI; J, TOMAZICALL; A, SHALLCROSS; J, TOMAZIC-ALLEN. "Mutant Escherichia coli alkaline phosphatase enzymes - having amino acid changes to increase specific activity while retaining thermal stability". Retrieved 1 May 2016. 
  10. ^ Maxam AM, Gilbert W (1980). "Sequencing end-labeled DNA with base-specific chemical cleavages". Meth. Enzymol. Methods in Enzymology. 65 (1): 499–560. doi:10.1016/S0076-6879(80)65059-9. ISBN 978-0-12-181965-1. PMID 6246368. 
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  14. ^ Jody A. Charnow, ed. (April 16, 2010). "Alkaline Phosphatase May Be a Marker of Inflammation in CKD Patients". Renal and Urology News. 
  15. ^ Badve, S. V., Zhang, L., Coombes, J. S., Pascoe, E. M., Cass, A., Clarke, P., ... on behalf of the HERO Study Collaborative Group (2015). "Association between serum alkaline phosphatase and primary resistance to erythropoiesis stimulating agents in chronic kidney disease: a secondary analysis of the HERO trial". Canadian Journal of Kidney Health and Disease. 2: 33. doi:10.1186/s40697-015-0066-5. 
  16. ^ Mizumori, M., Ham, M., Guth, P. H., Engel, E., Kaunitz, J. D., & Akiba, Y. (2009). "Intestinal alkaline phosphatase regulates protective surface microclimate pH in rat duodenum". The Journal of Physiology. 587 (Pt 14): 3651–3663. doi:10.1113/jphysiol.2009.172270. PMC 2742288Freely accessible. PMID 19451200. 
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  24. ^ C.R. Ganellin, David J. Triggle - 1996
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  29. ^ Chou, Janice Y.; Robinson, J. C. (1977-01-01). "Induction of Placental Alkaline Phosphatase in Choriocarcinoma Cells by 5-Bromo-2'-Deoxyuridine". In Vitro. 13 (7): 450–460. JSTOR 4291955. PMID 18400. 
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  33. ^ Vroon, David. "Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition". 
  34. ^ "Alkaline phosphatase: Liver Function Test - Viral Hepatitis". www.hepatitis.va.gov. Retrieved 2016-05-02. 
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  37. ^ Dugdale, David C. "ALP-bloodtest:MedlinePlus Medical Encyclopedia". MedlinePlus. Retrieved 2014-02-26. 
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  39. ^ Schiele F, Vincent-Viry M, Fournier B, Starck M, Siest G (November 1998). "Biological effects of eleven combined oral contraceptives on serum triglycerides, gamma-glutamyltransferase, alkaline phosphatase, bilirubin and other biochemical variables". Clin. Chem. Lab. Med. 36 (11): 871–8. doi:10.1515/CCLM.1998.153. PMID 9877094. 
  40. ^ Robinson, David; Sandblom, Gabriel; Johansson, Robert (Jan 2008). "Prediction of survival of metastatic prostate cancer based on early serial measurements of prostate specific antigen and alkaline phosphatase". Journal of Urology. 179 (1): 117–122. PMID 17997442. Retrieved 2 May 2016. 
  41. ^ Arceci RJ, Hann IM, Smith OP, eds. (2006). Pediatric hematology (3rd ed.). Wiley-Blackwell. p. 763. ISBN 978-1-4051-3400-2. 

External links[edit]

Further reading[edit]