Molecular action, of vitamin

Thomas, S.R., and Stocker, R., 2000, Molecular action of vitamin E in lipoprotein oxidation impheations for atherosclerosis. Free Radio. Biol. Med. 28 1795-1805. 

Jones G, Strugnell SA, and DeLuca HF (1998) Current understanding of the molecular actions of vitamin D. Physiological Reviews78, 1193-1231. 

Kirkwood s description is not wrong, but it is one-sided. His memorable simplicity conceals a can of worms. The molecular action of vitamin C is as simple and repetitive as flipping a coin, yet the effects are varied, unpredictable and utterly dependent on the milieu in which it operates. Just as flipping a coin leads to diametrically opposed outcomes, so too, vitamin C may on the one hand protect against illness and on the other kill tumours, or even people. The food chemist William Porter summed up the conundrum nicely, rising to an anguished eloquence rarely matched in scientific journals "Of all the paradoxical compounds, vitamin C probably tops the list. It is truly a two-headed Janus, a Dr Jekyll-Mr Hyde, an oxymoron of antioxidants."... 

Figure 17.1 The coagulation cascade., Site of action of vitamin K antagonists LMWH, low molecular weight heparin.

The mechanism of action of the vitamin D metabolites remains under active investigation. However, calcitriol is well established as the most potent agent with respect to stimulation of intestinal calcium and phosphate transport and bone resorption. Calcitriol appears to act on the intestine both by induction of new protein synthesis (eg, calcium-binding protein and TRPV6, an intestinal calcium channel) and by modulation of calcium flux across the brush border and basolateral membranes by a means that does not require new protein synthesis. The molecular action of calcitriol on bone has received less attention. However, like PTH, calcitriol can induce RANK ligand in osteoblasts and proteins such as osteocalcin, which may regulate the mineralization process. The metabolites 25(OH)D and 24,25(OH)2D are far less... 

Vogel S, Gamble MV, Blaner WS Retinoid uptake, metabolism and transport, in Nau H, BlanerWS (eds) The Handbook of Experimental Pharmacology, Retinoids The Biochemical and Molecular Basis of Vitamin A and Retinoid Action. Springer-Verlag, Heidelberg, 1999, pp. 31-96. 

Ross TK, Darwish HM, and DeLuca HF (1994) Molecular biology of vitamin D action. Vitamins and Hormones 49, 281-326. 

Hewison M, Zehnder D, Bland R, and Stewart PM (2000) lalpha-Hydroxylase and the action of vitamin D. Journal of Molecular Endocrinology 25,141-8. 

Thu molecular mechanism of action of vitamin A in the visual process has been under investigation for many years. Wald in 1(168 and Morton in 1972" characterized this mechanism of action. The chemistry of vision was reviewed comprehensively in Accotmi.t of Clwmical Research (1975) by numerous investigators. These reviews include theoretical studies of the visual chromophorc. characleri/alion of ihfldopsin in synthetic systems, dynamic processes in vertebrate rod visual pigments and their membranes, and the dynamics of the visual protein opsin. ""... 

Re.seaa-h since the mid-1980s has taken va.si strides in determining the molecular mechanism of action of vitamin A. It appears that the vitamin exerts its biological function with respect to development, diffcrcnlialion. and metabolism like a steroid hormone. The biologically active species is believed to be retinoic acid. Two intracellular retinoic acid-binding proteins have been isolated. CRABP(I) and CRABPfll). The.se appear to have functions similar to those of the CRBPs. 

Khanna, S., Roy, S., Ryu, H., Bahadduri, R, Swaan, RW, Ratan, R.R., and Sen, C.K., Molecular basis of vitamin E action. Tocotrienol modulates 12-lipoxygenase, a key mediator of glutamate-induced neurodegeneration, J. Biol. Chem. 2003. 

Figure 54.1 Warfarin and vitamin K. The dashed line in the vitamin K structure indicates a long hydrocarbon chain (20 carbon atoms in the side chain altogether). There is sufficient similarity in the ring structures of the two compounds for warfarin to act as a molecular mimic, thus counteracting the action of vitamin K (see Appendix 14).

General metabolic significance. Component of and interaction with biological membranes, protection of lipids against peroxidation, preservation of the membrane structure and integrity (exact molecular mechanism of vitamin E action unknown). 

Molecular Basis of Vitamin E Action Tocotrienol Modulates 12-Lipoxygenase, a Key Mediator of Glutamate-Induced Neurodegeneration,/. Biol. Chem. 278 43508—43515 (2003). 

Provitamin and vitamin D are liposoluble compounds, and their absorption in the intestine depends on lipid absorption. Intestinal diseases accompanied by pronounced steatorrhea result in vitamin D deficiency with osteomalacia and rickets. Although vitamin D was one of the first vitamins to be identified, it is only recently that its role in metabolism has been clarified. The mechanism of action of vitamin D raises problems at the histological and the molecular level Which tissues are the target of vitamin D What are the intricacies of the molecular reaction involving vitamin D in calcification ... 

---