Vitamin B7
Functions
Coenzyme for various carboxylase enzyme complexes, which all add a 1-carbon group
- Fatty acid synthesis: acetyl-CoA carboxylase
- Acetyl-CoA (2C) → malonyl-CoA (3C)
- Gluconeogenesis: pyruvate carboxylase
- Pyruvate (3C) → oxaloacetate (4C)
- Fatty acid reduction: propionyl-CoA carboxylase
- Propionyl-CoA (3C) → methylmalonyl-CoA (4C)
Tip
Biotin is a coenzyme in all carboxylase enzyme complexes that are not vitamin K-dependent.
Epidemiology
Etiology
- Malnutrition
- Prolonged use of antibiotics (destruction of intestinal flora)
- Excessive consumption of raw egg white: contains avidin → binds biotin in the intestinal lumen → inhibition of biotin resorption
- Like most proteins, avidin is heat-sensitive and loses this characteristic when cooked.
Pathophysiology
Clinical features
- Dermatitis
- Conjunctivitis
- Enteritis
- Alopecia
- Myalgia
- Neurological symptoms: lethargy, depression, mental status changes, hallucinations, paresthesia