1.5.4.i. Biotin, Choline, Inositol

Anti-egg-white Injury Factor

What is another name for biotin based on its interaction with raw egg white?

Vitamin H, Coenzyme R, and Bios II

What older names were used for biotin?

Micrograms (µg)

In what unit is biotin usually measured?

Carbon dioxide fixation and carboxylation reactions

What is the major coenzyme function of biotin?

Carboxylases

What type of enzymes require biotin as a coenzyme?

Fatty acids, purines, and pyrimidines

Biotin is important in the synthesis of which major compounds?

Carboxylation reactions, particularly those involved in fatty-acid and energy metabolism

Biotin works with acetyl-CoA in reactions involved primarily in what type of metabolism?

It is commonly bound to protein and released during digestion.

How is biotin present in many foods?

Avidin

What protein in raw egg white binds biotin and makes it unavailable for absorption?

Avidin binds biotin, preventing its absorption.

Why can habitual consumption of large amounts of raw egg whites cause biotin deficiency?

Yes. A small amount is synthesized by intestinal/colonic bacteria.

Does the intestine synthesize some biotin?

No. True deficiency is rare because biotin is widely available in foods and some is synthesized by intestinal bacteria.

Is dietary biotin deficiency common in humans?

Biotinidase deficiency

What inherited disorder prevents normal recycling of biotin?

An autosomal recessive disorder in which biotin cannot be efficiently released from proteins and recycled.

What is biotinidase deficiency?

Delayed growth and development, hearing loss, ataxia, seizures, coma, and potentially death

What manifestations may occur in children with severe biotinidase deficiency?

No known toxic effects were reported.

Has significant biotin toxicity been demonstrated in humans according to the text?

About 30 µg/day

What adult biotin intake is listed in the text?

About 20–25 µg/day

What biotin intake is listed for adolescents?

Liver and other glandular organs, meats, egg yolk, molasses, whole grains, legumes, nuts, and milk

What foods are particularly good sources of biotin?

A water-soluble essential nutrient commonly grouped with the B-complex vitamins

What type of nutrient is choline?

Acetylcholine

Choline is a precursor of which important neurotransmitter?

Phospholipids

Choline is an important component of what major class of membrane lipids?

Methionine

Which methyl-donor nutrient is closely related metabolically to choline?

Folate

Choline metabolism is also closely related to which vitamin involved in one-carbon metabolism?

Methyl groups (–CH₃)

What important biochemical group can choline donate?

It mobilizes fat and helps prevent excessive fat accumulation in the liver.

What is the major lipotropic function of choline?

It is incorporated into phospholipids, which are required for normal lipid transport and membrane structure.

Why is choline important in fat transport?

Lecithin, cephalin, and sphingomyelin

Which phospholipids listed in the text contain or are associated with choline?

It is a precursor of acetylcholine, which participates in nerve impulse transmission.

What is choline’s major role in nervous-system function?

Memory, intelligence/cognition, and mood

Which cognitive functions are associated with acetylcholine metabolism?

Through a specific choline transporter across the blood-brain barrier

How can choline enter the brain despite being poorly lipid-soluble?

Fatty liver

What is the major manifestation of choline deficiency described in the text?

Protein, particularly when methionine availability is inadequate.

Choline deficiency is especially associated with inadequate intake of what general nutrient?

Chronic alcoholism and kwashiorkor

What conditions mentioned in the text may be associated with choline-related fatty liver?

About 425–550 mg/day

What adult Adequate Intake range for choline is listed in the text?

Egg yolk

What is the richest food source of choline listed in the text?

Liver, brain, kidney, heart, meats, legumes, nuts, yeast, and wheat germ

What are other good dietary sources of choline?

Myo-inositol

What form of inositol is primarily utilized by the human body?

Muscle sugar

What older descriptive name is given to inositol because of its glucose-like structure?

Glucose

From what compound can the human body synthesize myo-inositol?

Phospholipids

Inositol is an important structural component of what class of compounds in animal cells?

Phytic acid (inositol hexaphosphate)

In what major form does inositol occur in plants?

It binds minerals such as calcium and iron, forming poorly soluble complexes that reduce absorption.

Why can phytic acid decrease mineral absorption?

It participates in phospholipid metabolism and fat transport.

What lipotropic role has been attributed to inositol?

Hexaniacinate

Which inositol derivative mentioned in the text has niacin-like activity?

Kidney

Which organ is described as a major site of myo-inositol catabolism?

No. A specific human deficiency syndrome has not been clearly demonstrated.

Has a clearly defined inositol deficiency syndrome been established in humans?

Alopecia

What deficiency manifestation is observed in experimental animals lacking inositol?

Humans can synthesize it endogenously, and a clear dietary requirement has not been established.

Why is there no established RDA for inositol?

About 1 g/day

What approximate daily intake of inositol is mentioned in the text?