Biotin availability and exceptional causes of deficiency
THE CONTEXT
Biotin is widely available from foods and intestinal synthesis; the passage identifies unusual circumstances in which deficiency occurs.
Sources and forms
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Biotin occurs widely in foods as biocytin, or ε-amino-biotinyl lysine, which is released on proteolysis.
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Intestinal flora synthesize biotin in excess of requirements.
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Carboxybiotin is identified as the active metabolic intermediate.
Circumstances associated with deficiency
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Biotin deficiency is described as unknown except in people maintained for many months on total parenteral nutrition and a very small number consuming abnormally large amounts of uncooked egg white.
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Uncooked egg white contains avidin, a protein that binds biotin and makes it unavailable for absorption.