vitamin B

from Wikipedia, the free encyclopedia

Vitamin B is the name for a group of vitamins that comprise eight water-soluble vitamins , all of which serve as precursors for coenzymes . They are chemically and pharmacologically completely different substances. The vitamins of the B group (also called B vitamins ) therefore do not represent a uniform class. The numbering is not continuous, because the vitamin character of many substances that were originally considered vitamins could not be confirmed.

The B vitamins are found in animal and vegetable foods (e.g. in fish, liver products, dairy products, broccoli, spinach or kale). An exception is vitamin B 12 , which is rarely found in plant foods, but, unlike all other water-soluble vitamins, can be stored in the body for a longer period of time.

history

At the beginning of the 20th century, the influence of different diets on the growth of mammals such as rats and mice was investigated. In 1912 Gowland Hopkins discovered that a lack of essential compounds, which he called “accessory food factors”, led to considerable growth disorders: “It is possible that what is absent from artificial diets and supplied by such addenda as milk and tissue extracts is of the nature of an organic complex (or of complexes) which the animal body cannot synthesize. " He suspected a connection between insufficient supply of these substances and similar health problems in humans, but did not investigate this further.

In 1912 the Polish biochemist Casimir Funk also worked intensively on isolating the active ingredient against the vitamin deficiency disease Beri-Beri , a hitherto inexplicable new disease that occurred in Japan and Java. This disease did not appear until after European rice husking machines were introduced in these countries. A deficiency disease was suspected. The Japanese doctor Takaki Kanehiro was able to cure the disease by adding the removed rice bran to the rice. Casimir Funk isolated a substance from rice bran that could cure the deficiency disease. Analysis of the compound showed that it was a nitrogen-containing compound , an amine . Based on these findings, Funk suggested the made-up word vitamins ( vita - life and amines ).

In 1913 Elmer McCollum - and independently Mendel with Osborne - succeeded in isolating the fat-soluble retinol . In 1916, McCollum introduced the categorization of vitamins by letter, in which he referred to retinol as "fat-soluble factor A". He also named a similar essential substance that he had extracted from wheat and rice bran as "water-soluble factor B".

In 1920, "factor A" and "factor B" became the names vitamin A and B, respectively, using the term already coined by Casimir Funk . McCollum later showed that vitamin B was not a single component but a complex.

The individual B vitamins

  • Vitamin B 1 is thiamine (aneurine). It consists of two heterocyclic rings, a pyrimidine ring and a thiazole ring, which are linked by a methylene group . The active form of vitamin B 1 is thiamine diphosphate (also thiamine pyrophosphate, TPP), which acts as a coenzyme (cocarboxylase) in the transfer of hydroxyalkyl residues (active aldehyde groups). The most important reactions of this type are the oxidative decarboxylation of 2-oxo acids and the transketolase reaction in the hexose monophosphate route. Thiamine was the first vitamin discovered about 100 years ago. A deficiency in vitamin B 1 leads to beriberi , a disease characterized by neurological disorders, heart failure, and muscle atrophy . It can also cause Korsakoff's syndrome , a form of amnesia (memory impairment) often observed in alcoholics .
  • Vitamin B 2 is riboflavin (lactoflavin), which serves as a precursor in the “yellow respiratory enzyme” for flavin coenzymes.
  • Vitamin B 3 is nicotinic acid (niacin). Niacin plays a role in the breakdown and build-up of nutrients, digestion, hormone production and blood circulation. A niacin deficiency ( e.g. in Pellagra ) is rare in Germany.
  • Vitamin B 5 is pantothenic acid , which plays an important role in the build-up and breakdown of carbohydrates, fats and the synthesis of cholesterol.
  • Vitamin B 6 is a collective name for pyridoxine (adermin), pyridoxamine and pyridoxal . The active form of these compounds is pyridoxal phosphate , the most important coenzyme in amino acid metabolism. Almost all conversion reactions of amino acids require pyridoxal phosphate, including transamination, decarboxylation, dehydration and the like. a. Also glycogen phosphorylase , an enzyme of glycogen degradation, including pyridoxal phosphate as a cofactor. A B 6 deficiency is rare.
  • Vitamin B 7 , also vitamin H, is biotin , which is essential as a cofactor of various carboxylase enzymes for the build-up and breakdown of carbohydrates, fats and proteins.
  • Vitamin B 9 , also vitamin B 11 or vitamin M is folic acid or folate. Folates are involved in many metabolic processes and are particularly important in cell division and growth processes (see also folinic acid ). More than 50 percent of Germans do not consume the recommended amount of 300 micrograms per day.
  • Vitamin B 12 is cobalamin (anti-pernicious vitamin). It is one of the most complex low molecular weight natural substances . The core of the molecule is a tetrapyrrole system ( Corrin ) with a cobalt ion as the central atom. The vitamin is synthesized exclusively by microorganisms . It is found particularly in liver, meat, eggs, milk and algae, but hardly in plant products ( occurrence ). The intestinal flora of the human large intestine does synthesize vitamin B 12 , but it can no longer be absorbed at this point and is excreted unused. Strict vegans should therefore supply the vitamin artificially and have its value checked regularly. Cobalamin can only be absorbed in the small intestine if the gastric mucosa secretes the so-called intrinsic factor (a glycoprotein) , which binds the cobalamin (the extrinsic factor) and thereby protects it from degradation. In the blood, the vitamin is bound to a special protein, the transcobalamin . The liver can store vitamin B 12 in amounts that are sufficient for several months - up to 3 to 5 years. That is why vitamin B12 supplements are useless for healthy people, because most of them would be excreted unused. A deficiency in vitamin B 12 is mostly due to the lack of the intrinsic factor and the resulting disturbance of absorption. The result is a disorder of blood formation, the so-called pernicious anemia , as well as neurological disorders ( funicular myelosis ). Cobalamin derivatives are primarily involved in rearrangement reactions in animal metabolism. They act e.g. B. as a coenzyme of the conversion of methylmalonyl-CoA to succinyl-CoA and the formation of methionine from homocysteine . In prokaryotes , cobalamin derivatives also contribute to the reduction of ribonucleotides.

A table with information on effects, occurrence, daily requirement and deficiency symptoms can be found in the article vitamin , section vitamin requirement and occurrence .

Related compounds and vitamin-like substances

Many of the following substances have been called vitamins because they were previously mistakenly believed to be. However, they are no longer considered as such. The numbers assigned to them now form the gaps in the series of B-complex vitamins described above. Vitamins B 4 , B 13 and B 15 are now vitamin-like substances and are known as vitaminoids, including other substances such as inositol (sometimes called "vitamin B8").

  • Vitamin B 4 is the vitamin-like substance choline which can be synthesized by the human organism and which, when it was wrongly considered a vitamin, was called B 4 .
  • Vitamin B 13 is orotic acid and used to be counted among the vitamins because it was previously assumed that orotic acid was essential for life. Orotic acid has many functions in the organism. Similar to choline (vitamin B 4 ), orotic acid can be synthesized in smaller quantities in the body itself, but must be taken in through food to meet daily needs.
  • Vitamin B 15 is the sodium salt of pangamic acid and was previously counted among the vitamins until it was found that the human organism can produce it in sufficient quantities itself. The physiological mechanism of action is not clearly understood.
  • "Vitamin B 17 " is not a vitamin, nor is it a substance that used to be counted among the vitamins, but a misleading fancy name for a glycoside that splits off hydric acid called amygdalin (a detailed critical examination of the medical use is dealt with in amygdalin).

literature

  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6th edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
  • Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
  • Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0-8153-4106-2 .

Individual evidence

  1. ↑ Ludwig Weissbecker: Diseases of the vitamin balance. In: Ludwig Heilmeyer (ed.): Textbook of internal medicine. Springer-Verlag, Berlin / Göttingen / Heidelberg 1955; 2nd edition, ibid. 1961, pp. 1083-1098, here: pp. 1090-1096.
  2. ↑ U. Dettmer, M. Folkerts, E. Kächler, A. Sönnichsen: Intensive course in biochemistry. Elsevier, Munich 2005, ISBN 3-437-44450-6 , p. 10.
  3. ↑ jameda Health Lexicon , accessed on November 25, 2015.
  4. ↑ James E. Darnell , Harvey Lodish, David Baltimore : Molecular Cell Biology . de Gruyter, Berlin et al. 2001, ISBN 3-11-011934-X (4th edition. Harvey Lodish: Molecular Cell Biology. Spectrum Academic Publishing House, Heidelberg et al. 2001, ISBN 3-8274-1077-0 ). (free full text access) .
  5. ↑ F. Rébeillé, S. Ravanel, A. Marquet, RR Mendel, ME Webb, AG Smith, MJ Warren: Roles of vitamins B5, B8, B9, B12 and molybdenum cofactor at cellular and organismal levels. In: Natural Product Reports . Volume 24, Number 5, October 2007, pp. 949-962, doi : 10.1039 / b703104c . PMID 17898891 .
  6. ↑ K. Pietrzik, I. Golly, D. Loew: Handbuch Vitamins. Urban & Fischer Verlag, Elsevier GmbH, Munich 2008; Pp. 147-154, 416; ISBN 978-3-437-55361-5
  7. ↑ Federal Institute for Risk Assessment of April 2, 2015