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Alkaline phosphatase

Alkaline phosphatase

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Encyclopedia
Alkaline phosphatase is a hydrolase
Hydrolase
In biochemistry, a hydrolase is an enzyme that catalyzes the hydrolysis of a chemical bond. For example, an enzyme that catalyzed the following reaction is a hydrolase:-Nomenclature:...

 enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 responsible for removing phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

 groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

. As the name suggests, alkaline phosphatases are most effective in an alkaline environment.
It is sometimes used synonymously as basic phosphatase.

Bacterial


In bacteria, alkaline phosphatase is located in the periplasmic space
Periplasmic space
The periplasmic space or periplasm is a space between the peptidoglycan cell wall and inner membrane of Gram-negative bacteria or the equivalent space outside the inner membrane of Gram-positive bacteria. It may constitute up to 40% of the total cell volume in Gram-negative species, and is...

, external to the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

. Since this space is much more subject to environmental variation than the actual interior of the cell, bacterial alkaline phosphatase is comparatively resistant to inactivation, denaturation
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...

, and degradation
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...

, and also has a higher rate of activity. Although the actual purpose of the enzyme is still not fully understood, the simple hypothesis, that it is a means for the bacteria to generate free phosphate groups for uptake and use, is supported by the fact that alkaline phosphatase is usually produced by the bacteria only during phosphate starvation and not when phosphate is plentiful. 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 in the wild. Some complexities of bacterial regulation
Regulation
Regulation is administrative legislation that constitutes or constrains rights and allocates responsibilities. It can be distinguished from primary legislation on the one hand and judge-made law on the other...

 and metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 suggest that other, more subtle, purposes for the enzyme may also play a role for the cell. In the laboratory
Laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...

, however, mutant
Mutant
In biology and especially genetics, a mutant is an individual, organism, or new genetic character, arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not...

 Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

lacking alkaline phosphatase survive quite well, as do mutants unable to shut off alkaline phosphatase production .

The optimal pH for the activity of the
E. coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

enzyme is 8.0 while the bovine
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

 enzyme optimum pH is slightly higher at 8.5.

Use in research


Typical use in the lab for alkaline phosphatases includes removing phosphate monoester to prevent self ligation.

Common alkaline phosphatases used in research include:
  • Shrimp alkaline phosphatase (SAP), from a species of Arctic shrimp
    Shrimp
    Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

     (Pandalus borealis
    Pandalus borealis
    Pandalus borealis is a species of shrimp found in cold parts of the Atlantic and Pacific Oceans. Many different common names are used, including pink shrimp, deepwater prawn, deep-sea prawn, great northern prawn, and northern shrimp.-Distribution:P...

    )
  • Calf-intestinal alkaline phosphatase (CIP)
  • Placenta
    Placenta
    The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

    l alkaline phosphatase (PALP) 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)


Alkaline phosphatase has become a useful tool in molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

 laboratories, since DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 normally possesses phosphate groups on the 5'
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 end. Removing these phosphates prevents the DNA from ligating
Ligation
Ligation may refer to:* In molecular biology, the covalent linking of two ends of DNA molecules using DNA ligase* In medicine, the making of a ligature * Chemical ligation, the production of peptides from amino acids...

 (the 5' end attaching to the 3'
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 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.

One common use in the dairy industry is as a marker of pasteurisation in cows' milk. This molecule is denatured by elevated temperatures found during pasteurisation, and can be tested for via colour change of a para-Nitrophenylphosphate
Para-Nitrophenylphosphate
para-Nitrophenylphosphate is a chromogenic substrate for acid and alkaline phosphatase in ELISA assays. Under their influence the decay to yellow para-nitrophenol is catalysed. This product can be measured with a 405 nm spectrophotometer....

 substrate in a buffered solution (Aschaffenburg Mullen Test). Raw milk would typically produce a yellow colouration within a couple of minutes, whereas properly pasteurised milk should show no change. There are of course exceptions to this in the case of heat-stable alkaline phophatases produced by some bacteria.

Inhibitors


All mammalian alkaline phosphatase isoenzymes except placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

l (PALP and SEAP) are inhibited by homoarginine, and, in similar manner, all except the intestinal and placental ones are blocked by levamisole
Levamisole
Levamisole is an anthelminthic and immunomodulator belonging to a class of synthetic imidazothiazole derivatives. It was discovered at Janssen Pharmaceutica in 1966...

. Heating for ~2 hours at 65°C inactivated most isoenzymes except Placental isoforms (PALP and SEAP).

Physiology


In humans, alkaline phosphatase is present in all tissues throughout the entire body, but is particularly concentrated in liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, bile duct
Bile duct
A bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...

, kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

, bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...

, and the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

. Humans and most other mammals contain the following alkaline phosphatase isozymes:
  • ALPI
    ALPI
    Alkaline phosphatase, intestinal also known as ALPI is a type of alkaline phosphatase that in humans is encoded by the ALPI gene....

     – intestinal
  • ALPL
    ALPL
    Alkaline phosphatase, tissue-nonspecific isozyme is an enzyme that in humans is encoded by the ALPL gene.- External Links :*-Further reading:...

     – tissue non-specific (liver/bone/kidney)
  • ALPP
    ALPP
    Alkaline phosphatase, placental type also known as placental alkaline phosphatase is an allosteric enzyme that in humans is encoded by the ALPP gene.- Gene :...

     – placental (Regan isozyme)

Diagnostic use


The normal range is 20 to 140 IU
International unit
In pharmacology, the International Unit is a unit of measurement for the amount of a substance, based on biological activity or effect. It is abbreviated as IU, as UI , or as IE...

/L. High ALP levels can show that the bile duct
Bile duct
A bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...

s are blocked. Levels are significantly higher in children and pregnant women. Also, elevated ALP indicates that there could be active bone formation occurring as ALP is a byproduct of osteoblast
Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...

 activity (such as the case in Paget's disease of bone
Paget's disease of bone
Paget's disease is a chronic disorder that can result in enlarged and misshapen bones. The excessive breakdown and formation of bone tissue causes affected bone to weaken, resulting in pain, misshapen bones, fractures, and arthritis in the joints near the affected bones...

).

Lowered levels of ALP are less common than elevated levels.

Elevated levels



If it is unclear why alkaline phosphatase is elevated, isoenzyme studies using electrophoresis
Electrophoresis
Electrophoresis, also called cataphoresis, is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. This electrokinetic phenomenon was observed for the first time in 1807 by Reuss , who noticed that the application of a constant electric...

 can confirm the source of the ALP. Heat stability also distinguishes bone and liver isoenzymes ("bone burns, liver lasts"). Placental alkaline phosphatase is elevated in seminomas.

Lowered levels


The following conditions or diseases may lead to reduced levels of alkaline phosphatase:
  • Hypophosphatasia
    Hypophosphatasia
    Hypophosphatasia is a rare, and sometimes fatal metabolic bone disease. Clinical symptoms are heterogeneous ranging from the rapidly fatal perinatal variant, with profound skeletal hypomineralization and respiratory compromise to a milder, progressive osteomalacia later in life...

    , an autosomal recessive disease
  • Postmenopausal
    Menopause
    Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...

     women receiving estrogen therapy
    Hormone replacement therapy (menopause)
    Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...

     because of osteoporosis
    Osteoporosis
    Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...

  • Men with recent heart surgery, malnutrition
    Malnutrition
    Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....

    , magnesium deficiency
    Hypomagnesemia
    Hypomagnesemia is an electrolyte disturbance in which there is an abnormally low level of magnesium in the blood. Usually a serum level less than 0.7 mmol/L is used as reference. The prefix hypo- means low . The middle 'magnes' refers to magnesium...

    , hypothyroidism
    Hypothyroidism
    Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...

    , or severe anemia
    Anemia
    Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

  • Children with achondroplasia
    Achondroplasia
    Achondroplasia dwarfism occurs as a sporadic mutation in approximately 85% of cases or may be inherited in an autosomal dominant genetic disorder that is a common cause of dwarfism...

     and cretinism
    Cretinism
    Cretinism is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones usually due to maternal hypothyroidism.-Etymology and use of cretin:...

  • Children after a severe episode of enteritis
    Enteritis
    In medicine, enteritis, from Greek words enteron and suffix -itis , refers to inflammation of the small intestine. It is most commonly caused by the ingestion of substances contaminated with pathogenic microorganisms. Symptoms include abdominal pain, cramping, diarrhea, dehydration and fever...

  • Pernicious anemia
    Pernicious anemia
    Pernicious anemia is one of many types of the larger family of megaloblastic anemias...

  • Aplastic anemia
    Aplastic anemia
    Aplastic anemia is a condition where bone marrow does not produce sufficient new cells to replenish blood cells. The condition, per its name, involves both aplasia and anemia...

  • Chronic myelogenous leukemia
    Chronic myelogenous leukemia
    Chronic myelogenous leukemia , also known as chronic granulocytic leukemia , is a cancer of the white blood cells. It is a form of leukemia characterized by the increased and unregulated growth of predominantly myeloid cells in the bone marrow and the accumulation of these cells in the blood...

  • Wilson's disease
    Wilson's disease
    Wilson's disease or hepatolenticular degeneration is an autosomal recessive genetic disorder in which copper accumulates in tissues; this manifests as neurological or psychiatric symptoms and liver disease...



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

Leukocyte alkaline phosphatase


Leukocyte alkaline phosphatase (LAP) is found within white blood cell
White blood cell
White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...

s. White blood cell levels of LAP can help in the diagnosis of certain conditions.
  • Higher levels are seen in polycythemia vera
    Polycythemia vera
    Polycythemia vera is a blood disorder in which the bone marrow makes too many red blood cells. It may also result in the overproduction of white blood cells and platelets. Most of the health concerns associated with polycythemia vera are caused by the blood being thicker as a result of the...

     (PV), essential thrombocytosis
    Essential thrombocytosis
    Essential thrombocythemia is a rare chronic blood disorder characterized by the overproduction of platelets by megakaryocytes in the bone marrow in the absence of an alternative cause. In some cases this disorder may be progressive, and rarely may evolve into acute myeloid leukemia or myelofibrosis...

     (ET), primary myelofibrosis (PM), and the leukemoid reaction
    Leukemoid reaction
    The term leukemoid reaction describes an elevated white blood cell count, or leukocytosis, that is a physiological response to stress or infection .It may be lymphoid or myeloid....

    .
  • Lower levels are found in chronic myelogenous leukemia
    Chronic myelogenous leukemia
    Chronic myelogenous leukemia , also known as chronic granulocytic leukemia , is a cancer of the white blood cells. It is a form of leukemia characterized by the increased and unregulated growth of predominantly myeloid cells in the bone marrow and the accumulation of these cells in the blood...

     (CML), paroxysmal nocturnal hemoglobinuria
    Paroxysmal nocturnal hemoglobinuria
    Paroxysmal nocturnal hemoglobinuria , sometimes referred to as Marchiafava-Micheli syndrome, is a rare, acquired, potentially life-threatening disease of the blood characterised by complement-induced intravascular hemolytic anemia , red urine and thrombosis...

     (PNH) and acute myelogenous leukaemia.

Further reading