Vitamin B7 (biotin) is said to be an essential cofactor for several enzymes involved in carboxylation reactions, e.g. pyruvate carboxylase and acetyl-CoA carboxylase, which catalyze key reactions in
gluconeogenesis, fatty acid metabolism, and
amino acid catabolism.
Biotin has an
imidazole ring fused with a
thiophane (tetrahydrothiophene) ring, which has a
pentanoic acid substituent attached .