Biotin biochemical function

Most vitamins function either as a hormone/ chemical messenger (cholecalciferol), structural component in some metabolic process (pantothenic acid), or a coenzyme (phytonadi-one, thiamine, riboflavin, niacin, pyridoxine, biotin, folic acid, cyanocobalamin). At least one vitamin has more than one biochemical role. Vitamin A as an aldehyde (retinal) is a structural component of the visual pigment rhodopsin and, in its acid form (retinoic acid), is a regulator of cell differentiation. The precise biochemical functions of ascorbic acid and a-tocopherol still are not well defined. 

The sulfur content in the human body is about 140 g. Foods contain a large number of covalent sulfur compounds. Many sulfur compounds perform important biochemical functions as biocatalysts (e.g. thiamine, pantothenic acid bound in coenzyme A and biotin), and sulfur-containing amino acids, cysteine and methionine, are protein constituents. Many sulfur compounds are important precursors of flavour-active compounds. 

Roffman, E., Meromsky, L., Ben-Hur, H., Bayer, E. A., and Wilchek, M. (1986) Selective labeling of functional groups on membrane proteins or glycoproteins using reactive biotin derivatives and 1-streptavidin. Biochem. Biophys. Res. Comm. 136, 80-85. 

Biotin (8.49), a thiophene-lactam, occurs in yeast, liver, kidney, eggs, vegetables, and nuts. It functions as a cocarboxylase in a number of biochemical reactions. It binds COj in the form of an unstable carbamic acid on one of the lactam nitrogens. The carbamate carboxyl is then donated easily. 

The problem is a functional deficiency of biotin, due both to inability to re-letise free biotin from dietary hiocytin tmd cdso to failure of the normal recovery of free biotin by biotinidase action on the hiocytin released by proteolysis of biotin-containing enzymes. Normal intcikes of biotin are inadequate to meet the requirements of these patients the provision of pharmacological doses of free biotin provides an adequate cunount to meet requirements without the need for reutilization. The delayed development of clinical and biochemical abnormalities is a result of the accumulation of biotin by the fetus, so that at birth the infant has adequate stores of the vitamin. 

To activate carbon dioxide for chemical reactions, it is advantageous to fix and destabilize this rather inert molecule. An important strategy to control and influence the reactivity of CO2 is its coordination to amines, metal-bound imido moieties, or metal centers (144), which leads to a decrease of the CO bond order, while the molecule in most cases becomes considerably bent. In biochemical pathways, the CO2 adduct of the coenzyme biotin (17) is involved in various carboxylation and transcarboxylation reactions (146). Similar structural motifs could become important functional building blocks for bioinspired photoreactions involving carbon dioxide activation steps (Fig. 18). 

CYPs have a role in bacteria to enable growth on carbon sources in the environment, such as on camphor by P. putida containing CYPlOl, or to undertake secondary metabolism as part of the biochemical warfare between organisms. Many CYPs are found in the pathways synthesizing important therapeutic compounds and this is discussed later in this chapter. The number of vital endogenous steps that have evolved for bacterial CYP function is still very small for instance, Biol in Bacillus subtilis is needed to produce biotin by a pathway distinct from other bacteria. Some CYPs, among the numerous forms uncovered, must be anticipated to be involved in key areas of endogenous metabolism especially in the... 

Vitamins are essential lead compounds for the development of novel radiopharmaceuticals. Many vitamin receptors such as the folate receptor are overexpressed on different tumor cell lines (Parker et al. 2005). Biotin labeled with Tc is under investigation since many years in different settings. A vitamin that has not found as much interest as hiotin is vitamin B12. Since it is a relatively large molecule, it has heen proposed to use B12 as a Trojan horse since rapidly proliferating cells and some bacterial stems show a high demand for this growth essential vitamin. While research toward labeled folate and B12 has intensified over the past couple of years, research with biotin rather slowed down. The biochemical pathways of folate and B12 are interlinked since folate delivers the -CH3 group to the apoenzyme in order to activate it toward its function in the methionine synthase cycle. 

As with many affinity tags, biotinylated tags can be positioned at either the N- or C-terminus of the protein to be arrayed, dependent on the structural and functional characteristics of the protein. In the context of oriented protein microarray fabrication, biochemical biotinylation seems preferable to chemical biotinylation since the latter offers little control over the site of biotinylation and still requires prepurification of each protein to remove excess biotinylation reagent. There are currently three main alternatives for biochemical introduction of a biotin moiety into a recombinant protein two involve affinity tags that can be biotinylated in vivo or in vitro whilst the third involves an intein-mediated introduction of biotinylated cysteine. 

Biotin deficiency implies biochemical and clinical disturbances of mammals vital functions. 

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