Each carboxylase catalyzes an essential metabolic reaction. Pyruvate carboxylase is a critical enzyme in gluconeogenesis, the formation of glucose from sources other than carbohydrates, for example, amino acids and fats. Methylcrotonyl-CoA carboxylase catalyzes an essential step in the metabolism of leucine, an indispensable amino acid .
Histones are proteins that bind to DNA and package it into compact structures to form chromosomes .
The compact packaging of DNA must be relaxed somewhat for DNA replication and transcription to occur. Avidin is a protein found in egg white, which binds biotin and prevents its absorption. Symptoms of overt biotin deficiency include hair loss and a scaly red rash around the eyes, nose, mouth, and genital area. Neurologic symptoms in adults have included depression, lethargy, hallucination, and numbness and tingling of the extremities. Biotinidase is an enzyme that catalyzes the release of biotin from small proteins and the amino acid, lysine, thereby recycling biotin.