Alkaline phosphatase

In humans, it is found in many forms depending on its origin within the body – it plays an integral role in metabolism within the liver and development within the skeleton.

Due to its widespread prevalence in these areas, its concentration in the bloodstream is used by diagnosticians as a biomarker in helping determine diagnoses such as hepatitis or osteomalacia.

[3][4] Additionally, abnormal levels of alkaline phosphatase in the blood could indicate issues relating to the liver, gall bladder or bones.

Since the periplasmic gap is more prone to environmental variation than the inner cell, alkaline phosphatase is suitably resistant to inactivation, denaturation, or degradation.

[6] The precise structure and function of the isozyme in E. coli is solely geared to supply a source of inorganic phosphate when the environment lacks this metabolite.

The mechanism of action of alkaline phosphatase involves the geometric coordination of the substrate between the Zn ions in the active sites.

Due to the kinetic energy induced by this temperature the weak hydrogen bonds and hydrophobic interactions of common proteins become degraded and therefore coalesce and precipitate.

However, upon dimerization of alkaline phosphatase, the bonds maintaining its secondary and tertiary structures are effectively buried such that they are not affected as much at this temperature.

Due to this, although it ultimately denatures at about 90 °C it has the added ability to accurately reform its bonds and return to its original structure and function once cooled back down.

[19] Typical uses in the lab for alkaline phosphatases include removing phosphate monoesters to prevent self-ligation, which is undesirable during plasmid DNA cloning.

[25] Alkaline phosphatase has become a useful tool in molecular biology laboratories, since DNA normally possesses phosphate groups on the 5' end.

This is because the most heat stable bacterium found in milk, Mycobacterium paratuberculosis, is destroyed by temperatures lower than those required to denature the enzyme.

Fluorimetry assays are required by milk producers in the UK to prove alkaline phosphatase has been denatured,[32] as p-Nitrophenylphosphate tests are not considered accurate enough to meet health standards.

[33] In addition, the Scharer Rapid Phosphatase test investigates the presence and the absence of ALP enzymes in raw milk.

However, positive test results in changing the raw milk color into blue, thus indicating the presence of ALP enzymes.

[38] In humans, alkaline phosphatase is present in all tissues throughout the body, but is particularly concentrated in the liver, bile duct, kidney, bone, intestinal mucosa and placenta.

[45] It dephosphorylates toxic/inflammatory microbial ligands like lipopolysaccharides (LPSs),[46] unmethylated cytosine-guanine dinucleotides, flagellin, and extracellular nucleotides such as uridine diphosphate or ATP.

Dephosphorylation of LPS by IAP can reduce the severity of Salmonella tryphimurium and Clostridioides difficile infection restoring normal gut microbiota.

[51] Furthermore, anionic nanocarriers exhibiting bioinert properties can alter their surface to interactive once having reached the intestinal epithelium as due to an alkaline phosphatase triggered cleavage of anionic phosphate groups from their surface charge converts to cationic improving for instance cellular uptake.

[53] 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.

[55] This explains why the addition of sodium butyrate show increased activity of alkaline phosphatase in the cancer cells of the human colon.

[2] In another study, choriocarcinoma cells were grown in the presence of 5-bromo-2'-deoxyuridine and results conveyed a 30- to 40-fold increase in alkaline phosphatase activity.

Skelphosphatase (which is localized in osteoblasts and extracellular layers of newly synthesized matrix) is released into circulation by a yet unclear mechanism.

Three metal ions, two Zn and one Mg, are contained in the catalytic sites, and both types are crucial for enzymatic activity to occur.

This explains why most salient structural features of mammalian alkaline are the way they are and reference their substrate specificity and homology to other members of the nucleoside pyrophosphatase/phosphodiesterase family of isozyme.