Avidin, biotin deficiency caused

Fig. 5 Metabolic blocks caused by biotin deficiencies. There are a small number of proteins that are biotinylated in vivo. Note that the naturally occurring biotin and biotinylated proteins may interfere with applications that use strept(avidin) on biological samples...

Biotin Deficiency. Relative to many of the vitamins, it is easy to induce a biotin deficiency by feeding volunteers raw egg white. Avidin, a basic protein found in egg white, forms salt linkages with acidic biotin and prevent its transport across the intestinal barrier. Cooked egg white is not a problem. Because biotin is found in the yolk, eating whole raw egg will not induce a deficiency. Deficiencies also were caused in patients on total parenteral nutrition (TPN) because biotin was not included in the early formulations. Symptoms include dermatitis, loss of hair color, and central neurological effects. 

Ans. Eggs are a rich source of biotin. However, egg white protein contains a protein called avidin which binds very strongly to biotin and this complex cannot be absorbed. A diet rich in egg white protein will cause a serious biotin deficiency. 

A few years later egg-white injury in chicks was shown to be associated with a deficiency of biotin in the tissues, despite its abundance in the diet [145]. In the same year, avidin was isolated from egg-white and its ability to inactivate biotin in vitro was demonstrated [146]. Gyorgy and Rose [235] fed rats with avidin but only found very small amounts of biotin in the faeces until the faeces were steamed. Biotin was then released from the avidin-biotin complex. As the result of further experiments, it was concluded that the fundamental cause of egg-white injury is the unavailability of biotin due to its fixation to avidin, so that biotin is not absorbed from the intestinal tract and is excreted in the faeces [237]. A similar conclusion was reached by Sullivan and Nicholls [603] who showed that when egg-white is cooked, avidin is denatured and rendered incapable of binding biotin. Egg-white injury has been produced experimentally in man and can be cured by the administration of biotin [607]. In a recent study, Peters [497] reported that raw egg-white has a direct toxic effect which is not associated with its action in causing biotin deficiency. It would appear, therefore, that further studies on egg-white injury must be more closely associated with a critical analysis of the different components of egg-white. 

Egg-white contains many different proteins and protein sub-fractions, each of which may act in one or more distinct ways both in vivo and in vitro. Thus although only the ovomucoid fraction elicits an anaphylactoid response in the rat, man of the protein components of egg-white are anaphylactic antigens. Moreover, although avidin causes biotin deficiency recent work suggests that egg-white injury may be attributable to an as yet unidentified fraction of egg-white. 

Concerning parenteral nutrition, the problem is the same but the existing formulas contain amino acids with adequate vitamin and mineral supplementation. Continuous consumption of raw eggs containing the protein avidin is well-known for causing biotin deficiency as the solid combination avidin/biotin is not absorbed. Nevertheless, such dietary intake is rather rare. Biotin deficiency can be considered as a public health problem in developing countries where severely malnourished children lack of multivitamins (Zempleni et al. 2008). 

Another of the water-soluble B vitamins known to have a function for some bacteria and animals is biotin. A role in carbohydrate metabolism has been suggested. A protein substance called avidin, when fed in the form of large amounts of raw egg yolk, combines with biotin, and may thus cause a biotin deficiency in some species. Somewhat similar symptoms have been reported in human subjects (Sydenstricker et al., 1942). Intestinal synthesis and the antivitamin may explain the failure to confirm this observation. No definite requirement for the diet can be stated. 

Biotin was discovered as a growth factor of yeast. Experiments with animals also produced deficiency symptoms (dermatitis, loss of hair) when avidin was administered. Avidin is a protein isolated from raw egg white that firmly binds biotin, and thus inactivates the vitamin. Excessive consumption of raw egg white apparently may cause biotin deficiency even in man. 

Finally it should be mentioned that nutritional deficiencies are not always caused by incomplete diets. A surplus of one nutritional element in the diet may result in the deficiency of another one. The disturbing substance may interfere with the absorption of an indispensable factor (avidin-biotin) or destroy it (thiamin by enzyme of fish) or inhibit it by displacing it from its normal r61e (vitamin inhibitors) (162). Metabolic disorders of the mother or increased demands of the offspring (twins) may in the presence of an adequate diet result in states of nutritional deficiency. 

A large daily intake of raw egg white (2 dozen eggs) contains sufficient avidin to cause deficiency fy binding biotin in the gastrointestinal tract... 

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