Cofactor for carboxylation enzymes (which add a 1-carbon group):- Pyruvate carboxylase: pyruvate (3C) → oxaloacetate (4C)- Acetyl-CoA carboxylase: acetyl CoA (2C) → malonyl-CoA (3C)- Propionyl-CoA carboxylase: proprionyl-CoA (3C) → methylmalonyl-CoA (4C)

Deficiency:- Relatively rare - Dermatitis, alopecia, enteritis- Caused by antibiotic use or excessive consumption of raw egg whites [contains avidin])