Carotenoid configurations

Fig. 2. Natural selection of carotenoid configuration in the reaction center (RC) and light-harvesting complex (LHC) of purple photosynthetic bacteria. See text for discussion. Figure source Koyama (1991) Structure and function of carotenoids in photosynthetic systems. J Photochem Photobiol, B Biol 9 208.

Koyama Y, Takatsuka I, Kanaji M, Tomimoto K, Kito M, Shimamura T, Yamashita J, Saiki K and Tsukida K (1990) Configurations of carotenoids in the reaction center and lightharvesting complex of Rhodospirillum rubrum. Natural selection of carotenoid configurations by pigment protein complexes. Photochem Photobiol 51 119-128... 

CD spectra of borohydride-treated and native Rb, sphaeroides R26 reaction centers are presented in Fig. 4. For comparison, the CD spectra of Rb, sphaeroides wild type strain 2.4.1 reaction centers are presented in Fig. 5. Because CD is a sensitive probe of the structure and environment of bound chromophores, it provides an opportunity to examine whether or not spheroidene is bound in the same manner for all the complexes. Furthermore, it is known that carotenoids are not optically active unless physically bound to the reaction center protein [8]. This is shown in Fig. 5 which demonstrates that spheroidene, incorporated into Triton X-100 micelles at a concentration equal to that of spheroidene bound to the reaction centers, does not display a CD spectrum. Upon binding to the reaction center protein, spheroidene becomes optically active, presumably either through exciton interactions with the amino acid residues in proximity to the chromophore or by an asymmetry in the carotenoid configuration or conformation, and displays a pronoimced CD spectrum. 

Bixin, a diapocarotenoid with a cis configuration at the carbon 9 and two carboxylic groups (one methylated), accounts for more than 80% of the total carotenoid content in annatto seeds, and has only been encountered to date in these seeds. The amount of red pigments in annatto seeds varies from 1.5 to 4%, depending on the variety. Bixin is the main pigment in commercial annatto powder... 

The carotenoid isomerase (CRTISO) was the first isomerase associated with the desaturation steps and named at a time when Z-ISO was unknown to exist ise.ws.ieo.iei (and reviewed in references ). In vitro analysis of substrate conversion " and transcript profiling in planta associated CRTISO with the desaturation steps. Isaacson demonstrated that CRTISO is specific for the 7,9 or 7,9- cis bond configuration and is not involved in the isomerization of the l5-l5-cis double bond to the trans conformation. As recently shown, Z-ISO is required for isomerization of the 15-15 cis double bond of phytoene produced in dark-grown tissues as well as in stressed photosynthetic tissues. Therefore, desaturation of phytoene to lycopene involves a two-step desaturation by PDS, followed l5-cis isomerization by Z-ISO, and then each pair of double bonds introduced by ZDS is followed by CRT-ISO-mediated isomerization of the resulting conjugated double bond pair. 

The determination of the absolute configuration of a carotenoid is only possible by circular dichroism (CD) measurement. The spectrum interpretation can only be done by comparison with reference or model compounds with known chiralities. The sample requirement is as low as 5 to 50 pg, but CD facilities are not so commonly available. Buchecker and Noack reported experimental aspects and discussion of the relationships of carotenoid structures and CD spectra. 

In all recorded spectra the 3Jee coupling constants between the olefinic protons are on the order of 11-12 Hz, proving the all-E configuration of the investigated carotenoids. Minor differences between the reported chemical shifts and literature data are due to the effect of different solvent compositions. 

Koyama, Y., Kito, M., Takii, T., Saili, K., Tsukida, K., and Yamashita, J. 1983. Configuration of the carotenoid in the reaction centers of photosynthetic bacteria. 2. Comparison of the resonance Raman lines of the reaction centers with those of the 14 different cis-trans isomers of (i-carotene. Photobiochem. Photobiophys. 5 139-150. 

Ruban, A.V., Pascal, A.A., Robert, B., and Horton, P. 2001. Configuration and dynamics of carotenoids in light-harvesting antennae of the thylakoid membrane. J. Biol. Chem. 276 24862-24870. 

Zsila, F., Z. Bikadi, J. Deh, and M. Simonyi. 2001d. Configuration of a single centre determines chirality of supramolecular carotenoid self-assembly. Tetrahedron Lett. 42 2561-2563. 

In addition, the results indicated that the efficiency of cis —> trans increased as the initial cis double bond configuration is shifted from the center of the polyenic chain, consistent with the 7j, triplet excited state potential curve that has a very shallow minimum at the 15-cis position compared to the deep minima at the all-trans position. The results strongly suggest that isomerization takes place via the 7j state of the carotenoid even in the case of direct photoexcitation, with their photosensitized process because of the very low intersystem crossing quantum yield, isc ([Pg.246]

Isoe, S., S. B. Hyeon, S. Katsumura et al. 1972. Photo-oxygenation of carotenoids. II. The absolute configuration of ioliolide and dihydroactinidioline. Tetrahed. Lett. 13 2517-2519. 

The first fully comprehensive coupling of NP and RP, where the previously described difficulties related to solvents immiscibility were overcome, was developed by Dugo et al. and applied to the analyses of oxygen heterocyclic components of lemon essential oils [22], Based on the configuration described in this work, other applications were developed for the analysis of carotenoids in citrus samples [48], citrus fruit extracts [29], pharmaceutical products [29], and triglycerides in fats and... 

Circular Dichroism. Several papersreport the use of c.d. correlations in establishing the absolute configurations of carotenoids. One report sounds a cautionary note since the signs of all maxima in the c.d. spectrum of 15-cw-(3S,3 5)-astaxanthin are opposite to those of the all-trani-isomer. 

The incorporation of " C-labelled neurosporene (138), lycopene, and y-carotene (141) into /3-carotene by cell extracts of Phycomyces blakesleeanus mutants has been demonstrated.Addition of unlabelled lycopene or /3-zeacarotene (140) caused approximately equal reduction of the incorpsration of [ C]neurosporene into /3-carotene, indicating that the alternative routes of Scheme 3 are of equivalent importance. The absolute configuration of C-6 of natural /3,y-carotene (55) is opposite to that of all C40 carotenoids with an e-ring end-group. " Opposite foldings of the aliphatic precursor are therefore required for cyclization to produce the y- and e-end-groups. 

The experimental configuration of the pump-probe experiment is similar to Ref. [5]. A home built non-collinear optical parametric amplifier (nc-OPA) was used as a pump, providing Fourier-transform-limited 30 fs pulses, which could be spectrally tuned between 480-560 nm. In all experiments white-light generated in a sapphire crystal using part of the fundamental laser (800 nm), was used as probe light. In the pump-probe experiments the pump was tuned to the S2 0-0 band for carotenoids with n>l 1. In the case of M9, it was not possible to tune the nc-OPA to its 0-0 transition, and hence another nc-OPA tuned to 900 nm was frequency doubled and used for excitation. In addition to conventional transient absorption pump-probe measurements, we introduce pump-deplete-probe spectroscopy, which is sensitive to the function of an absorbing state within the deactivation network. In this technique, we... 

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