The frequency of marginal biotin status is not known, but the incidence of low circulating biotin levels in alcoholics has been found to be much greater than in the general population. Also, relatively low levels of biotin have been reported in the urine or plasma of patients who have had a partial gastrectomyor have other causes of achlorhydria, burn patients, epileptics, elderly individuals, and athletes.^[20]Pregnancy and lactationmay be associated with an increased demand for biotin. In pregnancy, this may be due to a possible acceleration of biotin catabolism, whereas, in lactation, the higher demand has yet to be elucidated. Recent studies have shown marginal biotin deficiency can be present in human gestation, as evidenced by increased urinary excretion of 3-hydroxyisovaleric acid, decreased urinary excretion of biotin and bisnorbiotin, and decreased plasma concentration of biotin. Additionally, smoking may further accelerate biotin catabolism in women.^[21]

Biotin is also called vitamin H (the H represents Haar und Haut, German words for “hair and skin”) or vitamin B₇. Studies on its bioavailabilityhave been conducted in rats and in chicks. Based on these studies, biotin bioavailability may be low or variable, depending on the type of food being consumed. In general, biotin exists in food as protein-bound form or biocytin.^[19]Proteolysis by protease is required prior to absorption. This process assists free biotin release from biocytin and protein-bound biotin. The biotin present in corn is readily available; however, most grains have about a 20-40% bioavailability of biotin.^[20]

The wide variability in biotin bioavailability may be due to the ability of an organism to break various biotin-protein bonds from food. Whether an organism has an enzyme with that ability will determine the bioavailability of biotin from the foodstuff.^[20]

Biotin is consumed from a wide range of food sources in the diet, but few are particularly rich sources. Foods with a relatively high biotin content include Swiss chard, raw eggyolk(however, the consumption of avidin-containing egg whiteswith egg yolks minimizes the effectiveness of egg yolk's biotin in one's body), liver, Saskatoon berries, leafy green vegetables, and peanuts. The dietary biotin intake in Western populations has been estimated to be 35 to 70 μg/d (143–287 nmol/d).^[17]

Biotin is also available from supplements. The synthetic process developed by Leo Sternbachand Moses Wolf Goldbergin the 1940s uses fumaric acidas a starting material.^[18]

D-(+)-Biotin is a cofactorresponsible for carbon dioxidetransfer in several carboxylaseenzymes:

Acetyl-CoA carboxylase alpha

Acetyl-CoA carboxylase beta

Methylcrotonyl-CoA carboxylase

Propionyl-CoA carboxylase

Pyruvate carboxylase

Biotin is important in fatty acid synthesis, branched-chain amino acid catabolism, and gluconeogenesis. It covalently attaches to the epsilon-amino group of specific lysine residues in these carboxylases. This biotinylationreaction requires ATPand is catalyzed by holocarboxylase synthetase.^[12]In bacteria, biotin is attached to biotin carboxyl carrier protein (BCCP) by biotin protein ligase (BirA in E. coli).^[13]The attachment of biotin to various chemical sites, biotinylation, is used as an important laboratory technique to study various processes, including protein localization, protein interactions, DNAtranscription, and replication. Biotinidase itself is known to be able to biotinylate histone proteins,^[14]but little biotin is found naturally attached to chromatin.

Biotin binds very tightly to the tetrameric protein avidin(also streptavidinand neutravidin), with a dissociation constantK_d on the order of 10⁻¹⁵M, which is one of the strongest known protein-ligand interactions.^[15]This is often used in different biotechnological applications. Until 2005, very harsh conditions were thought to be required to break the biotin-streptavidin bond.^[16]

Biotin has an unusual structure (see above figure), with two rings fused together via one of their sides. The two rings are ureido and thiophenemoieties. Biotin is a heterocyclic, S-containing monocarboxylic acid. It is made from two precursors, alanineand pimeloyl-CoA via three enzymes. 8-Amino-7-oxopelargonic acid synthase is a pyridoxal 5'-phosphateenzyme. The pimeloyl-CoA, could be produced by a modified fatty acid pathway involving a malonyl thioester as the starter. 7,8Diaminopelargonic acid (DAPA) aminotransferase is unusual in using S-adenosyl methionine(SAM) as the NH₂ donor. Dethiobiotin synthethase catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP. Biotin synthase reductively cleaves SAM into a deoxyadenosyl radical—a first radical formed on dethiobiotin is trapped by the sulfur donor, which was found to be the iron-sulfur (Fe-S) center contained in the enzyme.^[11]

Fuyang Kexing Biochem Co.,Ltd. is a hi-tech joint-stock company limited. Located near Hangzhou, our company, set up by serveral professors of Zhejiang University, is mainly engaged in the R&D, production and sales of pharmaceutical intermediates and APIs.In 1998, our company was appraised as a "hi-and new-tech enterprise" in Zhejiang province, and it is one of the earliest private enterprises who enjoy the right to manage its import and export business. It has ever been awarded the Hanghzou municipal "Golden dragon medal " for exporting goods to earn foreign currency and been honored as one of the "top foreign currency earning enterprise" in Fuyang city. Currently, our Coenzyme Q10 series, health products and intermediates have enjoyed high reputation in the US, Europe and southeast Asia.
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