Exogenous carotenoids

A. Incorporation of Exogenous Carotenoids into Reaction Centers from Carotenoidless Mutants...237... 

Boucher et al. (1977) were the first to report that exogenous carotenoids could be incorporated into RCs from carotenoidless bacteria. Using the G9 strain from Ri. rubrum, these authors demonstrated that four carotenoids, spirilloxanthin, spheroidene, spheroidenone and chloroxanthin could be incorporated with nearly 1 1 mol ratios with respect to the primary donor (P 870). The authors showed that the bound carotenoids protected BChl against photodynamic bleaching. An analysis of the absorption and circular dichroism (CD) spectra of the bound carotenoids lead the authors to conclude that the carotenoids adopted a central mono-c/v configuration, a conclusion later confirmed by X-ray diffraction studies on Rhodopseudomonas viridis and Rb. sphaeroides (Yeates et al., 1988 Amoux, 1989 Deisenhofer and Michel, 1989 Ermler et al. 1994 Chapter 6, Fritsch). 

Strzalka, K. and W.I. Gruszecki. 1997. Modulation of thylakoid membrane fluidity by exogenously added carotenoids. J. Biochem. Mol. Biol. Biophys. 1 103-108. 

Research on carotenoids and cardiovascular disease (CVD) stems from the discovery that the etiology of this disease involves oxidative processes that may be slowed by exogenous antioxidants. One of the best understood processes contributing to development of CVD is the oxidation of low-density lipoprotein (LDL). When LDL becomes oxidized, it is readily taken up by foam cells in the vascular endothelium where it contributes to the development of atherosclerotic lesion. Enhancement of the oxidative stability of LDL may also prevent other oxidative steps involved in clinical expression of coronary disease (e.g., myocardial infarction) and possibly steps not related to LDL oxidation. There is optimism about the potential role of P-carotene in prevention of CVD... 

Vitamins are essential nutrients, which must be supplied exogenously. They are organic compounds with indispensable biological activities as coenzymes in a multitude of cellular metabolic processes. Vitamin A, retinoids (vitamin A-derivatives), carotenoids, vitamin D, vitamin E, and vitamin K are fat-soluble, vitamin C and vitamins of the B-complex are water-soluble. This is of importance for gastrointestinal absorption in oral supplementation as well as the transdermal penetration for topical applications. 

The hexane-extracted particles that still retained one Q per P700 retained 81 % of the NADP -reduction activity ofthe unextracted control. In contrast, particles extracted with hexane-0.3% methanol had all the OQ removed and the NADP -reduction activity was completely lost. The NADP -reduction activity of the hexane/methanol-extracted particles could be reactivated by readdition of exogenous but only when the hexane extract was also added back. Exogenous OQ alone, even at a rather high concentration, could not reactivate NADP photoreduction and the hexane extract alone was also not effective, presumably because of its low Q content. The nature ofthe component in the hexane extract that contributes to reconstitution is as yet unknown. As the hexane extract contains OQ,chlorophylls,carotenoids,lipidsand other nonpolar molecules, some critical component is probably needed to ensure the correct membrane structure for binding ferredoxin and/or Fd-NADP -reductase. This conclusion is supported by the fact that activity of prior terminal acceptors such as the iron-sulfur centers do not require the hexane extract. 

Marova, 1., Breierova, E., Kocf, R., Friedl, Z., Slovak, B., and Pokorna, J. 2004. Influence of exogenous stress factors on prodnction of carotenoids by some strains of carotenogenic yeasts. Ann Microbiol 54 73-85. 

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