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Biotin is a colorless, water-soluble B-complex vitamin that is also referred to as vitamin B₇.^1-3 Biotin functions as a cofactor for five mammalian enzymes that catalyze specific carboxylation reactions.² These are:

• Acetyl-CoA carboxylase I and II: catalyze the carboxylation of acetyl CoA to form malonyl CoA which, in turn, serves as a substrate for fatty acid elongation. These enzymes function in cytosolic fatty acid synthesis and in regulating mitochondrial fatty acid oxidation.

• Pyruvate carboxylase: catalyzes the carboxylation of pyruvate to form oxaloacetate, which serves as an intermediate in the citric acid cycle. This reaction is involved in gluconeogenesis, the production of glucose from other carbohydrates by the liver, kidney, and other gluconeogenic tissues.

• Methylcrotonyl-CoA carboxylase: catalyzes an essential step in the catabolism of leucine, an essential, branch-chained amino acid.

• Propionyl-CoA carboxylase: catalyzes essential steps in the metabolism of several amino acids, cholesterol, and odd chain fatty acids.¹

Biotin is also covalently attached to histone proteins that are essential for the folding of DNA into chromatin. It has been suggested that the biotinylation of histones might play a role in cell proliferation, gene silencing, and cellular response to DNA damage.⁴