Category: biosynthesis
Biotin = vitamin B7, cofactor for the FOUR mammalian carboxylases: pyruvate carboxylase (PC, gluconeogenesis anaplerosis), acetyl-CoA carboxylase (ACC, fatty acid synthesis rate-limiting), propionyl-CoA carboxylase (PCC, BCAA + odd-chain FA), methylcrotonyl-CoA carboxylase (MCC, leucine catabolism). Biotin is covalently attached to apo-carboxylases by HCS (holocarboxylase synthetase) on a specific lysine. Recycled by BIOTINIDASE that cleaves biotin from biotinyl-lysine (biocytin). Biotinidase deficiency = newborn-screened multiple carboxylase deficiency presenting with alopecia + seizures + cutaneous rash + metabolic acidosis; treated with oral biotin. Biotin supplementation (high doses for "hair + nails") interferes with biotin-streptavidin immunoassays — causes spurious lab results (TSH, troponin, hCG).