E-N-Biotinyl-L-lysine,

Biotin can be synthesized by the human colon flora. The question to which extent this production contributes to covering the host-organism s requirements is, however, subject to discussion. In most foods of animal origin as well as in cereals, biotin prevails in the protein (= enzyme)-bound form as e-N-biotinyl-L-lysine (= biocytin). Brewer s yeast, liver, soya beans, and peanuts number among the biotin rich foods [1]. 

Biocytin is e-N-biotinyl-L-lysine, a derivative of D-biotin containing a lysine group coupled at its e-amino side chain to the valeric acid carboxylate. It is a naturally occurring complex of biotin that is typically found in serum and urine, and probably represents breakdown products of recycling biotinylated proteins. The enzyme biotinidase specifically cleaves the lysine residue and releases the biotin component from biocytin (Ebrahim and Dakshinamurti, 1986, 1987). 

Dethiobiotin, the sulfur-free analog of biotin, competitively inhibits the growth of O. danica the inhibition index is 10. Biocytin (e-N-biotinyl-L-lysine) stoichiometrically replaced biotin for O. danica. Because O. danica is phagotrophic (A2), it can probably ingest low-molecular forms of biotin, e.g., biocytin. Other forms of biotin were not studied. 

Chemical structure (Figure 12). Biotin (hexahydro-2-oxo-lH-thieno[3,4-d]imidazole-4-pentanoic acid). Biologically active analogs biocytin (e-N-biotinyl-L-lysine), oxybiotin (S substituted by O). 

The biochemical MS assay performance was studied for various biotin derivatives, such as biotin [m/z 245), N-biotinyl-6-aminocaproic acid hydrazide (m/z 372), biotin-hydrazide (m/z 259), N-biotinyl-L-lysine (m/z 373) and biotin-N-succinimi-dylester m/z 342). These five different bioactive compounds were consecutively injected into the biochemical MS assay. Figure 5.12 shows triplicate injections in the biochemical MS-based system of the different active compounds. Each compound binds to streptavidin, hence the MS responses of peaks of the reporter ligand (fluorescein-biotin, m/z 390) are similar. The use of SIM allows specific components to be selected and monitored, e.g. protonated molecule of the biotin derivatives. In this case, no peaks were observed for biotin-N-succinimidylester (m/z 342), because under the applied conditions fragmentation occurred to m/z 245. In combination with full-scan MS measurements, the molecular mass of active compounds can be determined simultaneously to the biochemical measurement. 

Biotin enzymes carboxylases that use biotin as a cofactor. The biotin is bound via an amide bond to the E-amino group of a specific lysine residue in the enzyme protein, i.e. B.e. contain a biotinyllysyl residue. Free (+)-E-V-biotinyl-L-lysine actually occurs in yeast extract, and is known as biocytin. During catalysis, N-atom 1 of the biotin residue is carboxylated in an ATP-dependent reaction ATP + HCOj" + bioti-nyl-enzyme (I) -> ADP + Pj + carboxybiotinyl-en-zyme (II). The carboxyl group is then transferred from (II) to the carboxylase substrate (II) + substrate —> (I) + carboxylated substrate. 

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