Vitamin molecular function

A specific role for vitamin E in a required metabolic function has not been found. In addition to its direct antioxidant effects, a-tocopherol has been reported to have specific molecular functions. 

Azzi A, Ricciarelli R, and Zingg JM (2002) Non-antioxidant molecular functions of alpha-tocopherol (vitamin E). FEES Letters 519, 8-10. 

The molecular mechanism through which vitamin A functions in visual system is known as Rhodopsin cycle or Wald s visual cycle for which George Wald was awarded Nobel Prize. 

In the body, vitamin E functions as an antioxidant, trapping peroxy radicals of the type HOO and ROO formed as a result of enzymemolecular oxygen of the unsaturated hydrocarbon chains in membrane phospholipids. There is speculation that peroxy radicals play a role in the aging process and that vitamin E and other antioxidants may retard that process. Vitamin E is also necessary for the proper development and function of the membranes of red blood cells. 

Low-molecular-weight products, generally secondary metabolites such as alcohols, carboxyhc and an iino acids, antibiotics, and vitamins, can be recovered using many of the standard operations such as liquid-hquid extraction, adsorption and ion-exchange, described elsewhere in this handbook. Proteins require special attention, however, as they are sufficiently more complex, their function depending on the integrity of a delicate three-dimensional tertiaiy structure that can be disrupted if the protein is not handled correctly. For this reason, this section focuses primarily on protein separations. Cell separations, as a necessary part of the downstrean i processing sequence, are also covered. 

The structure of vitamin E in its most active form, o-tocopherol, is shown in Figure 18.38. a-Tocopherol is a potent antioxidant, and its function in animals and humans is often ascribed to this property. On the other hand, the molecular details of its function are almost entirely unknown. One possible role for... 

In 1922, Evans and Bishop named the animal nutritional factor essential of reproduction Vitamin E . In the 1960s, vitamin E was associated with antioxidant function. Twenty-five years later, vitamin E has been found to possess functions that are independent of its antioxidant and free radical scavenging ability. a-Tocopherol specific molecular mechanisms were discovered which are still under investigation. 

Szklarz GD, Graham SE, Paulsen MD. Molecular modeling of mammalian cytochromes P450 application to study enzyme function. Vitamins Hormones 2000 58 53-87. 

Fluorescent probes are divided in two categories, i.e., intrinsic and extrinsic probes. Tryptophan is the most widely used intrinsic probe. The absorption spectrum, centered at 280 nm, displays two overlapping absorbance transitions. In contrast, the fluorescence emission spectrum is broad and is characterized by a large Stokes shift, which varies with the polarity of the environment. The fluorescence emission peak is at about 350 nm in water but the peak shifts to about 315 nm in nonpolar media, such as within the hydrophobic core of folded proteins. Vitamin A, located in milk fat globules, may be used as an intrinsic probe to follow, for example, the changes of triglyceride physical state as a function of temperature [20]. Extrinsic probes are used to characterize molecular events when intrinsic fluorophores are absent or are so numerous that the interpretation of the data becomes ambiguous. Extrinsic probes may also be used to obtain additional or complementary information from a specific macromolecular domain or from an oil water interface. 

RPE plays numerous functions essential for proper structure and function of retinal photoreceptors. They include the maintenance of the blood-retina barrier, selective uptake and transport of nutrients from the blood to the retina and removal of waste products to the blood, enzymatic cleavage of P-carotene into vitamin A, storage of vitamin A and its metabolic transformations, phagocytosis and molecular renewal of POS, expression and secretion of growth factors and immunomodulatory cytokines (Aizman et al., 2007 Aleman et al., 2001 Crane et al., 2000a,b Elner et al., 2006 Holtkamp et al., 2001 Leuenberger et al., 2001 Lindqvist and Andersson, 2002 Maminishkis et al., 2006 Momma et al., 2003 Strauss, 2005). 

Rajan, D. P., et al. Human placental sodium-dependent vitamin C transporter (SVCT2) molecular cloning and transport function. Biochem. Biophys. Res. Commun. 1999, 262, 762-768. 

The health sciences are a group of disciplines that draw upon chemistry, physics, and biology. How does chemistry relate to the health sciences Knowing about molecular structure and function allows biochemists to synthesize medicinal compounds on a large scale, and even to design new molecules to fight diseases and their symptoms. Understanding the chemical role of nutrients, vitamins, and minerals in the body helps... 

Phototherapy is the generic term covering therapies which use light either with or without a sensitiser. Those that do not require a sensitiser use the natural chromophores within the tissue to perform this function e.g. treatment of vitamin D deficiency in rickets, and neonatal jaundice). Those that do use an added sensitiser include photochemotherapy (largely psoriasis and skin disorders) and photodynamic therapy (currently mainly cancer). Photodynamic therapy is differentiated from photochemotherapy by its additional requirement for the presence of oxygen at molecular or ambient levels.In this text we will deal only with photodynamic therapy since, at the present time, this is the main driving force in phototherapy. ° ... 

An interesting and fimctionally important aspect of transcriptional activators is that one and the same protein can act as both an activator and a repressor. The alternative functionality is determined by the sequence environment, the presence of other transcriptional activators (steroid receptors, see ch. 4), by specific repressors or by low molecular weight effectors. Examples are the receptors for vitamin A acid, which, in the absence of its ligand, represses the genes with cognate DNA elements. TTie repression is exerted in the DNA-bound form. In the presence of its hgand, vitamin A acid, the same receptor acts as a transcriptional activator (see ch. 4). 

PRECURSOR. In biological systems, an intermediate compound or molecular complex present in a living organism which, when activated physiochemically, is converted to a specific functional substance. Sometimes the prefix pro is used to indicate that a compound in question plays the role of a precursor. Examples from the history of vitamin and other essential chemical developments include ergosterol (pro-vitamin D2), which is activated by ultraviolet radiation to form vitamin D carotene (provitamin A) is a precursor of vitamin A prothrombin forms thrombin upon activation in the blood-clotting mechanism. 

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