Once biotinylated, three halocarboxylases (hCBXs) are localised to the mitochondrial matrix. The mechanism of transfer is still unclear. Pyruvate carboxylase (PC) is required for gluconeogenesis, lipogenesis, neurotransmitter synthesis and insulin secretion; Methylcrotonyl-CoA carboxylase (MCC) is required for amino acid metabolism; propionyl-CoA carboxylase (PCC) is required for odd-chain fatty acid oxidation (Ingaramo & Beckett 2012, Hiratsuka et al. 1998, Bailey et al. 2010).