Biotin functions

Biotin functions to transfer carbon dioxide in a small number of carboxylation reactions. A holocarboxylase synthetase acts on a lysine residue of the apoenzymes of acetyl-CoA carboxylase, pymvate carboxylase, propi-onyl-CoA carboxylase, or methylcrotonyl-CoA carboxylase to react with free biotin to form the biocytin residue of the holoenzyme. The reactive intermediate is 1-7V-carboxybiocytin, formed from bicarbonate in an ATP-dependent reaction. The carboxyl group is then transferred to the substrate for carboxylation (Figure 21—1). 

L. Haussling, H. Ringsdorf, F.J. Schimitt, and W. Knoll, Biotin-functionalized self-assembled monolayers on gold-surface-plasmon optical studies of specific recognition reactions. Langmuir 7, 1837-184 (1991). 

Figure 3.4 Structure of two prosthetic groups (a) biotin (b) lipoate. Biotin functions as a carboxyl group carrier, e.g. in acetyl-CoA carboxylase. Lipoate is presented in its oxidised form (-S-S-). It is a cofactor for pyruvate dehydrogenase and oxoglu-tarate dehydrogenase.

The third approach made use of the streptavidin-biotin couple to connect enzymes to hydrophobic polymer tails (Figure 6.11c) [36]. In the first step of the self-assembly, two biotin-functionalized polystyrene chains (90 repeat units, PDI =... 

Several useful schemes for attaching nucleic acid probes onto electrode surfaces have thus been developed [2-8]. The exact immobilization protocol often depends on the electrode material used for signal transduction. Common probe immobilization schemes include attachment of biotin-functionalized probes to avidin-coated surfaces [15], self-assembly of organized monolayers of thiol-functionalized probes onto gold transducers [16], carbodiimide covalent binding to an activated surface [17], as well as adsorptive accumulation onto carbon-paste or thick-film carbon electrodes [15-30]. 

Aslan, K. and Perez-Luna, V. H. (2006). Nonradiative Interactions between Biotin Functionalized Gold Nanoparticles and Fluorophore-Labeled Antibiotin/ /asmonto 1 111-119. 

Biotin forms part of several enzyme systems and is necessary for normal growth and body function. Biotin functions as a cofactor for enzymes involved in carbon dioxide fixation and transfer. These reactions are important in the metaboHsm of carbohydrates, fats, and proteins, as well as promotion of the synthesis and formation of nicotinic acid, fatty acids, glycogen, and amino acids (5—7). Biotin is absorbed unchanged in the upper part of the small intestine and distributed to all tissues. Highest concentrations are found in the Hver and kidneys. Little information is available on the transport and storage of biotin in humans or animals. A biotin level in urine of approximately 160 nmol/24 h or 70 nmol/L, and a circulating level in blood, plasma, or serum of approximately 1500 pmol/L seems to indicate an adequate supply of biotin for humans. However, reported levels for biotin in the blood and urine vary widely and are not a reHable indicator of nutritional status. 

Figure 17. Schematic representation of the affinity biosensor construction and the proposed operational principle and voltammetric traces for affinity sensor signalling a biotin-functionalized surface before (A) and after (B) target protein (antibiotin IgG-HRP) association and precipitation reaction steps. Voltammetric measurements were performed in 0.1 M phosphate buffer (pH 7.0),containing 0.1 mM ferrocene methanol as a signal tracer. Inset charge coupled device (CCD) camera images of a sensor surface upon signalling reactions (Adapted from Refs. [176] [177]).

Ghenciu EG, Beckman EJ. Affinity extraction into carbon dioxide. 1. Extraction of avidin using a biotin-functional fluoroether surfactant. Ind Eng Chem Res 1997 36 5366-5370. 

Haussling L, Michel B, Ringsdorf H and Rohrer H 1991 Direct observation of streptavidin specifically adsorbed on biotin-functionalized self-assembled monolayers with the scanning tunneling microscope Angew. Chem. Int. Edn. Engl. 30 569-72... 

Biotin, which does not contain a phosphate group, is covalently bound to a lysine in enzymes called carboxylases (see Fig. 8.12B). Its functional group is a nitrogen atom that covalently binds a CO2 group in an energy-requiring reaction. This bound CO2 group is activated for addition to another molecule. In the human, biotin functions only in carboxylation reactions. 

Delwiche, E. A. Biotin function in succinic acid decarboxylation by... 

In an analogous manner, a carboxyl group may also be transferred to propionyl-CoA (for the biosynthesis of branched or odd-numbered fatty acids, isoleucine synthesis, or cholesterol metabolism) or to 3-methylcrotonyl-CoA (a degradation product of leucine after addition of water, there results hydroxymethyl-glutaryl-CoA, the precursor of mevalonic acid cf. section 7.1.2). [117] Oxaloacetic acid is derived from pyruvate, which is of central importance for gluco-neogenesis. [108] In addition, biotin participates also in the transfer of carboxylic acid functions. In prokaryotes, biotin functions as a cofactor for decarboxylases (Tab. 7.6). 

Mouffouk, E, S.J. Brown, A.M. Demetriou, S.J. Higgins, R.J. Nichols, R.M.G. Rajapakse, and S. Reeman. 2005. Electrosynthesis and characterization of biotin-functionalized poly(terthiophene) copolymers, and their response to avidin. / Mater Chem 15 1186-1196. 

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