Intestines biotin

Two children with the late-onset form initially were reported as having a defect in intestinal transport of biotin. This conclusion was supported by finding low plasma biotin concentrations when these children were administered oral biotin compared to the concentrations of plasma biotin of unaffected control subject. In 1983, it was demonstrated that the primary biochemical defect in most patients with late-onset multiple carboxylase deficiency was a deficiency of serum biotinidase activity. The two children with a putative defect in intestinal biotin transport both were confirmed to have biotinidase deficiency. This disparity was reconciled by demonstrating that, in both cases, the children were biotin depleted at the time the biotin-loading studies were performed. Therefore, when the children initially were given biotin, although the vitamin was transported into the blood normally, it was rapidly taken up... 

Chatterjee NS, Kumar CK, Ortiz A, Rubin SA, and Said HM (1999) Molecular mechanism of the intestinal biotin transport process. American Journal of Physiology 277, C605-13. 

Ramaswamy K (1999) Intestinal absorption of water-soluble vitamins focus on molecular mechanism ofthe intestinal biotin titLnspottprocess. AmericanJournalofPhysiology 277, C603-4. 

Said, H.M., 2009. Cell and molecular aspects of human intestinal biotin absorption. The Journal of Nutrition. 138 158-162. 

Subramanian, S.B., Subramanian, V.S., Kumar, J.S., Hoiness, R., and Said H.M., 2011b. Inhibition of intestinal biotin absorption by chronic alcohol feeding cellular and molecular mechanisms. American Journal of Physiology. Gastrointestinal and Liver Physiology. 300 G494—501. 

Recently, Prasad et al. cloned a mammalian Na+-dependent multivitamin transporter (SMVT) from rat placenta [305], This transporter is very highly expressed in intestine and transports pantothenate, biotin, and lipoate [305, 306]. Additionally, it has been suggested that there are other specific transport systems for more water-soluble vitamins. Takanaga et al. [307] demonstrated that nicotinic acid is absorbed by two independent active transport mechanisms from small intestine one is a proton cotransporter and the other an anion antiporter. These nicotinic acid related transporters are capable of taking up monocarboxylic acid-like drugs such as valproic acid, salicylic acid, and penicillins [5], Also, more water-soluble transporters were discovered as Huang and Swann [308] reported the possible occurrence of high-affinity riboflavin transporter(s) on the microvillous membrane. 

Spontaneous biotin deficiency is unlikely to occur as a result of simple dietary restriction, since biotin has high potency, is widely distributed in foods, and is also synthesized in the intestine. The human requirement for biotin is not known, but subjects on a low-biotin diet recovered in 3-5 days, when 75-300 jxg biotin was administered daily (S23, S24). 

Ng, K.-Y. and Borchardt, R.T., Biotin transport in a human intestinal epithelial cell line (Caco-2), Life Sci., 53, 1121, 1993. 

Vitamin H (biotin) is present in liver, egg yolk, and other foods it is also synthesized by the intestinal flora. In the body, biotin is covalently attached via a lysine side chain to enzymes that catalyze carboxylation reactions. Biotin-dependent carboxylases include pyruvate carboxylase (see p. 154) and acetyl-CoA carboxylase (see p. 162). CO2 binds, using up ATP, to one of the two N atoms of biotin, from which it is transferred to the acceptor (see p. 108). 

Biotin cannot be synthesized by mammals. The contribution of the biotin synthesized by intestinal bacteria to the hnman reqnirements is still controversial. Biotin is an essential cofactor for carboxylases involved in prodnction of fatty acids, cell growth, and metabolism of fats and amino acids. 

By Biotin Soybeans and other legumes, egg yolks, nuts, and organ meats it is also produced naturally in the body by intestinal bacteria <1 yr 5-6 pg 1-19 yr from 8 to 25 pg >19 yr 30 pg pregnancy 30 pg lactating women 35 pg... 

Biotin (vitamin B ) is widespread in foods and is also synthesized by intestinal bacteria. It is a coenzyme for the carboxylation of pyruvate, acetyl-coenzyme-A (CoA), propionyl CoA, and /1-methyl-crotonyl CoA and is involved in fatty acid formation and in energy release from carbohydrates. In humans deficiencies only occur in patients with an abnormal gut flora and manifests itself as exfoliative dermatitis and alopecia. 

Biotin required for growth and normal function by animals, yeast, and many bacteria is seldom found in deficiency in humans because the intestinal bacteria synthesize it in sufficient quantity to meet requirements. Biotin deficiency does occur, however, 111 animals fed raw whiles of eggs. The egg white contains a protein, avidin, which combines with biotin, and tins complex is not broken down by enzymes of the gastrointestinal tract. Hence, a deficiency develops. 

Serum biotinidase activity is not altered by biotin deficiency. This was demonstrated by finding normal serum biotinidase activity in several patients who became biotin deficient while being treated with parenteral hyperalimentation lacking biotin. Biotinidase appears to play an important role in the processing of protein-bound biotin, either by being secreted into the intestinal tract, where it can release biotin from... 

An important factor in biotin s availability is that some of the vitamin is derived from synthesis by intestinal microorganisms this is demonstrated by the fact that three to six... 

Other proteins that interact with biotin including egg yolk biotinbinding proteins and biotin transport components from several systems including yeast, mammalian intestinal cells, and bacteria [70-73]. Note that although there are other proteins (e.g., fibropellins) that have a motif [DENY]-jc(2)-[KRI]-[STA]-x(2)-V-G-jc-[DN]-jc[FW]-T-[KR] in common with strept(avidin), most if not all of these protein do not bind biotin (http //www.expasy.org/prosite/). 

Biotin -member of the B-complex family Water soluble Metabolism of fats synthesis of ascorbic acid healthy skin hair balding and greying. Soya beans, brown rice, nuts, fruit, brewer s yeast and milk. It can be synthesised by intestinal bacteria. 100 pg No... 

Dietary deficiency of biotin sufficient to cause clinical signs is extremely rare in human beings, although it may be a problem in intensively reared poultry. However, there is increasing evidence that suboptimal biotin status may be relatively common, despite the fact that the vitamin is widely distributed in many foods, is synthesized by intestinal flora, and there is an efficient mechanism for conserving biotin after the catabolism of biotin-containing enzymes. 

Most biotin in foods is present as biocytin, incorporated into enzymes, which is released on proteolysis, then hydrolyzed by biotinidase in the pancreatic juice and intestinal mucosal secretions to yield free biotin. Biocytin is not absorbed to any significant extent. 

Biotin uptake into enterocytes is by a sodium-dependent carrier, which also transports pantothenic acid (Section 12.2) and lipoic acid, but is inhibited by biocytin and dethiobiotin. The carrier is found in both the small intestine and the colon, so both biotin and pantothenic acid synthesized by intestinal bacteria can be absorbed (Chatterjee etal., 1999 Ramaswamy, 1999 Said, 1999 Prasad and Ganapathy, 2000). Even at relatively high intakes (up to 80 /rmol), biotin is more-or-less completely absorbed (Zempleni and Mock, 1999b). 

The brush border of the kidney cortex has a sodium-biotin cotransport system similar to that in the intestinal mucosa, thus providing for reabsorption of free biotin filtered into the urine. It is only when this mechanism is saturated (it has a relatively low K n) that there will be a significant excretion of biotin. 

As a result of this resorption and the protein binding of plasma biotin, which reduces filtration at the glomerulus, renal clearance of biotin is only 40% of that of creatinine. This efficient conservation of biotin, together with the recycling of biocytin released from the catabolism of biotin-containing enzymes, may be as important as intestinal bacterial synthesis of the vitamin in explaining the rarity of deficiency. 

Biocytin is hydrolyzed by biotinidase, which acts on free or peptide-incorporated biocytin to release biotin, but has no general peptidase or esterase activity. Biotinidase is most active toward free biocytin, but it will also release biotin from biocytin-containing peptides. The activity decreases as the size of the peptide increases, so it is likely that in vivo the catabolism of biotin-containing enzymes is by proteolysis, followed by biotinidase action, rather than the release of biotin, leaving the apoenzyme as a substrate for proteolysis. Biotinidase is found in all tissues, including the pancreatic juice and intestinal mucosa. 

Biotin is essential for cell proliferation. Peripheral blood mononuclear cells appear to take up biotin by a system that is distinct from the sodium-dependent multivitamin transporter that is responsible for intestinal and renal uptake of biotin (Section 11.1). In response to mitogenic stimuli the uptake of biotin increases several-fold, with no change in the activity of the sodium-dependent transporter. At the same time, there is an increase in the rate of expression of methylcrotonyl CoA, propionyl CoA carboxylases, and holocarboxylase... 

Birds are especially sensitive to biotin deficiency, at least partly because their intestinal flora make little or no contribution to biotin intake. This is of considerable commercial importance with intensively reared poultry. In adult birds, biotin deficiency does not affect egg production, but does reduce the amount of biotin in the eggs, thus impairing embryonic development. In severe deficiency, the hatchability of the eggs can fall to near zero. 

On the basis of studies in patients who developed deficiency during total parenteral nutrition, and who are therefore presumably wholly reliant on an exogenous source of the vitamin - with no significant contribution from intestinal bacterial synthesis - the provision of 60 fxg of biotin per day for adults receiving total parenteral nutrition is generally recommended (Bitsch et al., 1985). 

The intestinal absorption of pantothenic acid is by use of the same sodium-dependent carrier as biotin and lipoic acid (Section 11.1). The carrier is found throughout the intestinal tract, and therefore pantothenic acid synthesized by intestinal bacteria (Section 12.2.4) will, like biotin, be available for absorption (Said et al., 1998 Chatterjee et al., 1999 Ramaswamy, 1999 Said, 1999 Prasad... 

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