Biotin syntheses

R. L. Baxter, and L. Sawyer. Biotin synthesis requires three other enzymes (steps b, c, d). Step b is catalyzed by a PLP-dependent transaminase. At the left is thiamin diphosphate, in the form of its 2-(1 -hydroxyethyl) derivative, an intermediate in the enzyme pyruvate decarboxylase (Dobritzsch et al.,. Biol. Chem. 273,20196-20204,1998). Courtesy of Guoguang Lu. Thiamin diphosphate functions in all living organisms to cleave C-C bonds adjacent to C=O groups. 

Repressors may have similar recognition domains but may vary greatly both in size and in the functioning of their other domains, which may react both with small allosteric effectors and with other proteins. The repressor BirA of the E. coli biotin synthesis operon is an enzyme. The 321-residue protein activates biotin to form biotinyl 5 -adenylate and transfers the biotinyl group to proteins such as acetyl-CoA carboxylase107-1093 and also represses transcription. 

Comebactena flavum m biotin synthesis [VITAMINS - BIOTIN] (Vol 25)... 

Biotin Synthesis Sulfur Preempts a Beckmann Rearrangement... 

The hydroxyoxathiapane 21, a precursor in a new biotin synthesis, is readily obtained by cyclization (Equation 9) <2001JOC6197>. 

The thiazole ring is synthesized from a pentulose or deoxypentulose 5-phosphate and either glycine or tryptophan, depending on the organism. Incorporation of sulfur leads to formation of hydroxymethyl thiazole, which is then phosphorylated. The sulfur comes from cysteine and is incorporated by formation of a thiocarboxylate at the carboxyl terminal of the enzyme, unlike biotin synthesis (Section 11.1.1), where an iron-sulfur cluster at the active site of the enzyme is the donor. 

Biotin is bound covalently to enzymes by a peptide fink to the s -amino group of a lysine residue, forrningbiotinyl-s-arnino-lysine orbiocytin (see Figure 11.1). This postsynthetic modification is catalyzed by holocarboxylase synthetase with the intermediate formation of biotinyl-5 -AMP. In bacteria, this intermediate also acts as a potent repressor of all four enzymes of biotin synthesis. 

In Streptomyces, it is assumed that streptavidin htis an tmtibiotic role it is secreted together with a low moleculrir weight inhibitor of biotin synthesis, stra-vidin. It has been suggested that avidin in eggs has a similtu role, to protect the developing embryo from (biotin-requiring) bacteria that penetrate the shell. Alternatively, because cells in culture can take up and utilize avidin-biotin. 

Syntheses and applications of l,3-dihydro-2//-imidazol-2-one in biotin synthesis 04KFZ(5)28. 

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