Vitamin syntheses

Antibiotics (qv) have been fed at subtherapeutic levels to promote mminant animal growth. Possible reasons for the observed growth include decreased activity of microbes having a pathogenic effect on the animal, decreased production of microbial toxins, decreased microbial destmction of essential nutrients, increased vitamin synthesis or synthesis of other growth factors, and increased nutrient absorption because of a thinner intestinal wall... 

Vinyl triflones 636 Vitamins, synthesis of 833 VSEPR theory 34... 

DellaPenna, D. and Pogson, B.J., Vitamin synthesis in plants tocopherols and carotenoids, Annu. Rev. Plant Biol. 57, 711, 2006. 

The reaction can be used on a laboratory scale in vitamin synthesis. The enantioselectivity of this method lies in the same range as that observed in the catalytic hydrogenation of structurally related substrates. In contrast with chiral Rh or Ru complex-mediated catalytic hydrogenation, reduction of a,/ -... 

Paran I, Van Der Knaap E (2007) Genetic and molecular regulation of fruit and plant domestication traits in tomato and pepper. J Exp Bot 58 3841-3852 Wang D, Bosland P (2006) The genes of Capsicum. HortScience 41 1169-1187 DellaPenna D, Pogson BJ (2006) Vitamin synthesis in plants tocopherols and carotenoids. Annu Rev Plant Biol 57 711-738... 

A healthy diet usually covers average daily vitamin requirements. By contrast, malnutrition, malnourishment (e.g., an unbalanced diet in older people, malnourishment in alcoholics, ready meals), or resorption disturbances lead to an inadequate supply of vitamins from which hypovitaminosis, or in extreme cases avitaminosis, can result. Medical treatments that kill the intestinal flora—e. g., antibiotics—can also lead to vitamin deficiencies (K, Bi2, H) due to the absence of bacterial vitamin synthesis. 

Vitamin D is a fat-soluble vitamin. The vitamin is closely associated with sunlight, as periodic exposure to sunlight can eliminate the dietary requirement for the vitamin. The pathway for vitamin synthesis in animals requires a light-dependent step the opening of an aromatic ring, resulting in conversion of a precursor of the vitamin to vitamin . Failure to obtain exposure to sunshine can result in the... 

Three previously healthy workers who worked in a plant that supplied chemicals for vitamin synthesis were hospitalized with liver injury following 2-4 months of exposure to a mixture of chemicals that included lipophilic and hydrophilic components ... 

Feedback repression is the inhibition of formation of one or more enzymes in a pathway by a derivative of the end product. In many (but not all) amino acid biosynthetic pathways, the amino add end product must first combine with its transfer RNA (tRNA) before it can cause repression. Feedback repression is a widespread regulatory device especially for the synthesis of molecules intended for incorporation into macromolecules, e.g. amino adds, purines, and pyrimidines. Synthesis of vitamins also appears to be controlled by feedback repression, as well as by catabolite regulation (Birnbaum et al, 1967 Sasaki, 1965 Newell and Tucker, 1966 Wilson and Pardee, 1962 Papiska and Lichstein, 1968). Regulation of vitamin synthesis is important since only a small number (probably about 1000) of vitamin molecules are required per cell whereas many molecules of an average amino acid (probably 50 million) are required. An extremely wasteful case of vitamin overproduction would develop if enzymes for vitamin synthesis were produced at the same rate and were as active as the amino acid biosynthetic enzymes. 

As already mentioned, this process had disadvantages, and great efforts were made to improve it. The production of etinol was described as early as 1948 as the most expensive and difficult part of this vitamin synthesis, and the situation had hardly changed by the early 1980s. 

Competitive inhibitors that block enzyme reactions in a parasite are potent chemotherapeutic agents. Eor example, sulfanilamide will block folic acid (a B vitamin) synthesis, and the resulting... 

If substances spare the B vitamins by increasing vitamin synthesis, or by reducing metabolic requirements, they should act equally well when given parenterally. Ekman and Strcimbeck (1949) reported that rats survived a very short while longer on riboflavin-deficient diets when they were injected with small doses of ascorbic acid, though there was no difference in the appearance of the signs of deficiency. If these results are confirmed, they would imply that ascorbic acid can indeed reduce the metabolic need for riboflavin, but only to a very limited extent. 

Finally, although there seems to be no specific organism or organisms (joncerned with vitamin synthesis, it is likely that some particular patterns of microflora are more conducive to synthesis than others. We should then expect to find that the case with which animals may be made independent of dietary B vitamins would vary from laboratory to laboratory, and from time 1.0 time. This indeed has been the history of starch refection over the thirty-five years since it was first described. We may recall that, two or three years after Fridericia announced the discovery of the phenomenon of starch refection, it was denied by Mendel and Vickery (1929) because they could not repeat it. 

The Chemistry and Biochemistry of Vitamin Synthesis of Novel Analogues of Vitamin B ... 

The beneficial effect of mycobacterial culture liquid was due to its content of amino acids, vitamins, peptides, and possibly of specific stimulators of vitamin synthesis, since the vitamin content of the cells was increased to a greater extent than their biomass. Although amino acids exert a significant effect on the synthesis of vitamin Bn, the complete culture liquid of mycobacteria was more effective, which can be explained by the complex influence of many metabolites released by mycobacteria in the exponential phase of growth. Of special interest are polypeptides secreted by mycobacteria into the medium, which may have a specific stimulatory effect on vitamin Bn biosynthesis. Chromatographic separation of mycobacterial polypeptides is shown in Fig. 4.23B. Specific stimulatory effects were displayed by fractions 10, 11 and 12. 

Hill, M.J. 1997. Intestinal flora and endogenous vitamin synthesis. EurJ Cancer Prev 6, S43-S45. 

Although vitamin synthesis will be discussed elsewhere, it should be noted that just as the bacteria of the ruminant and other herbivores synthesize vitamins in substantial amounts, so it is highly probable that in man vitamins K, B complex, and E are synthesized in amoimts which help to meet requirement. Indeed some evidence for this already exists. On the other hand, certain intestinal bacteria destroy vitamins, e.g., vitamin C and nicotinic acid. 

The intestinal ecosystem is a complex microenvironment constituted by eukaryotic and prokaryotic cells where a complex network of signals that maintain the intestinal homeostasis is established. The gut microbiota is an important component of this ecosystem commensal bactaia are key players participating in the digestion process, vitamin synthesis, and other metabolite production (bile acids, lipids, amino acids, and short-chain fatty acids), which are important for maintaining health in mammals (Brestoff and Artis 2013). However, it is known that the commensal microbiota is not in direct contact with the epithelial cells due to the presence of the mucus layer (Johansson et al. 2011). 

Biotechnological production of vitamins using LAB as an alternative to chemical vitamin synthesis has been under study for more than a decade (Taranto et al. 2003 De Angelis et al. 2014 see also... 

XVII. Vitamin Synthesis and Its Impucations in Hubian Nutrition... 

The phenomenon of vitamin synthesis by bacteria presents important considerations in the nutrition of man. Its full significance, however, should await a more complete knowledge of the human need for the B vitamins than we now possess. At the present time, we are certain that at least part of our requirements are furnished by bacterial action in the intestines. It is, therefore, comforting to know that we can at least rely to some extent on this mechanism to supplement the average American diet should the ever persistent vitamin vendor fail in his benevolent task. 

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