Biotin B7

egg white injury

biotin was discovered based on research on…

hair loss, dermatitis, and neuromuscular problems

what happened when you would eat excessive amounts of raw eggs?

biotin

this vitamin is widely distributed in foods, with beef, soybeans, and egg yolks being excellent sources.

avidin

also known as an anti-vitamin, it can bind with biotin preventing its absorption.

it is found in raw egg whites.

one molecule of this anti-vitamin binds 4 molecules of biotin (very strong and irreversible binding).

keratin

biotin is used to help stimulate _________ synthesis.

biocytin

biotin bound to a lysine residue; this is the protein-bound form that can be digested.

carboxylation

what is the coenzyme role of biotin?

non-coenzyme roles

biotinylation of histones (unraveling), transcription factors can reach DNA promoter sequences; gene expression.

pyruvate carboxylase

converts pyruvate to oxaloacetate

replenishes oxaloacetate for TCA cycle; necessary for gluconeogenesis

its involved in carboxylase reactions (glucose metabolism)

acetyl-CoA carboxylase

forms malonyl-CoA from acetate; commits acetate units to fatty acid synthesis

It is a rate limiting step of FA biosynthesis

propionyl-CoA carboxylase

converts propionyl-CoA to methylmalonyl-CoA; provides mechanism for metabolism of some amino acids and odd-number-chain FAs.

ß-methylcrotonyl-CoA carboxylase

converts ß-methylcrotonyl-CoA to ß-methylglutaconyl-CoA; allows catabolism of leucine and certain isoprenoid compounds.

the biotin cycle

free biotin provides biotin to the various apocarboxylases.

holocarboxylase synthetase assembles active holocarboxylases by covalently binding biotin to their active sites.

the holocarboxylases are then degraded proteolytically to biocytin or small biotinyl-peptides.

these compounds are further cleaved by biotinidase to produce lysine and free biotin, which can enter the free biotin pool, thereby recycling the vitamin.

biotinylation

the attachment of biotin to apocarboxylase is called…

holocarboxylase

refers to biotin attached to any of four carboxylases.

true

t/f

deficiencies of biotin are rare, but they can be very serious if it occurs.

holocarboxylase synthase deficiency

symptoms include lethargy, depression, dermatitis, and hallucinations.

risk groups of biotin deficiency

biotinidase/holocarboxylase synthase deficiency

excessive ingestion of raw egg whites

pregnant, breastfeeding women

alcoholic disorders

GI disorders that impair absorption (IBS)