Phytyl chain

Figure 23-28 (A) Model of a light-harvesting chlorosome from green photosynthetic sulfur bacteria such as Chlorobium tepidum and species of Prosthecochloris. The chlorosome is attached to the cytoplasmic membrane via a baseplate, which contains the additional antenna bacteriochlorophylls (795 BChl a) and is adjacent to the trimeric BChl protein shown in (B) and near the reaction center. After Li et al.302 and Remigy et a/.304 (B) Alpha carbon diagram of the polypeptide backbone and seven bound BChl a molecules in one subunit of the trimeric protein from the green photosynthetic bacterium Prosthecochloris. For clarity, the magnesium atoms, the chlorophyll ring substituents, and the phytyl chains, except for the first bond, are omitted. The direction of view is from the three-fold axis, which is horizontal, toward the exterior of the molecule. From Fenna and Matthews.305 See also Li et al.302...

The bacteriochlorophyll a protein from the green phot osynthetic bacterium Prosthecochloris aestuarii has been determined at 2.8 A resolution.389 It is made up of three identical subunits, tightly packed around a three-fold symmetry axis. Each subunit consists of a core of seven bacteriochlorophyll a molecules enclosed within a bag of protein. There are extensive contacts between the phytyl chains of the seven bacteriochlorophylls within each subunit. These tails form an inner hydrophobic core. The seven magnesiums appear to be five-coordinate. In five cases the fifth ligand is a histidine side-chain, in one case a protein backbone carbonyl oxygen, and in the other case a water molecule. It appears that the removal of one or more of the bacteriochlorophyll molecules would destabilize the protein. It is unlikely that the chlorophyll can be reversibly removed from the protein. 

In plastids of etiolated radish seedlings, far-red light stimulated the synthesis of all prenyl chains, but it did not alter the relative concentrations of the various chains synthesized under dark conditions. White light further stimulated chain synthesis, particularly the formation of phytyl chains,370 and a similar situation occurred with barley.371 In contrast, both far-red and white light changed the pattern of carotenoid synthesis in etioplasts of Raphanus seedlings372 and it seems that phytochrome in its excited state controls light-induced synthesis of carotenoid. This synthesis was also... 

Vitamin K Uptake and Metabolism. Dietary vitamin and the pharmaceutical form, phytonadione or vitamin K go) must be converted to the K2 series known as menoquinones. The most common of these is menoquinone-4 or K2(20)> This conversion to the K2 series occurs in the liver and possibly the intestinal flora. It involves removing the phytyl chain producing the intermediate menadione. Menadione sometimes is prescribed when there is impaired uptake of lipids from the intestine. There is little storage reserve in the liver, and a deficiency can result when dietary intake of vitamin K is restricted or absorption is impaired. 

Fig. 4. (A) The side view of the LHC-II monomer in the membrane (lipid bilayer). The chlorophyll molecules are oriented nearly perpendicular to the membrane plane (the phytyl chains are omitted for clarity). Two lutein molecules form an internal X-shaped brace. (B) A sketch of the amino-acid sequence of the LHC-II polypeptide and a listing of the known Chl-residue ligation. White letters inside black circles indicate amino-acid ligands to the chlorophylls [also see legend on the right side of (B)]. Note that the model in (B) is rotated 90° with respect to that in (A) about an axis normal to the membrane. Figure source (A) Kuhibrandt, Wang and Fujiyoshi (1994) Atomic model of plant light-harvesting complex by electron crystallography. Nature 367 618 and 620.

On the other hand. Biggins examined various benzo-, naphtho- and anthraquinones and found a more stringent structural requirement for areplacement quinone to be functional at the A i site. It was specifically noted that among the many types of quinones, only naphthoquinones possessing a hydrocarbon chain at the 3-position, namely, 2-methyl-3-decyl-, 2-methyl-3-(isoprenyl)2- and 2-methyl-3-(isoprenyl)4-naphthoquinones, similar to phylloquinone with the 3-phytyl chain, could provide the required molecular structure for interaction with the hydrophobic domain at the A site, as confirmed by the criterion of P700 /P430 recombination kinetics. All other quinones presumably could oxidize Aq but the reduced quinone then recombined directly with P700. It was also noted that 2,3-dimethyl-1,4-naphthoquinone,... 

Ghosh, S., Lee, S. J., Ito, K. et al. (2000). Molecular recognition on giant vesicles coating of phytyl phosphate vesicles with a polysaccharide bearing phytyl chains. Chemical Communications, pp. 267-8. 

Fig. 5.12 Biological oxidation pathways involved in the degradation of phytyl chains (after Rontani et al. 1999).

Fig. 8. Superposition of the special pairs of the RCs from Rb. sphaeroides (shown in Color Plate 8 in red) and Rp. viridis (shown in Color Plate 8 in green) represented without their phytyl chains, left View perpendicular to the planes of the macrocycles, right View rotated by 90°. The superposition shows the high degree of structural identity of both RCs. As shown in b, the ester methyl groups of ring V have different orientations in both RCs. (See also Color Plate 8)...

Fig. 7-3, Structure illustrating the chlorophyll-a-water-chlorophyll-a interaction. The dimensions of the ring and the phytyl chain are not to scale. [Reproduced by permission from K. Ballschmiter and J. J. Katz, J. Amer. Chem. Soc., 1969, 91, 2661.]...

In this the magnesium is replaced by a copper atom and the phytyl chain has been removed. Chlorophyll c (28) is of marine origin. 

Fig. 8. Proposed structure for the photoactive chlorophyll a dimer in which the carbonyl oxygen on ring V is hydrogen bonded. R is the phytyl chain. R can be a hydrogen atom or an alkyl group. It has been postulated that X could be 0, N, or S. (From Ref. 68.)... 

Samples isolated by the HPLC may be further characterized by either electron impact or tandem mass spectroscopy. High-resolution mass spectroscopic analysis of a-tocotrienol shows a molecular ion peak M+ at m/z 424, which corresponds to the molecular formula C29H44O2. Fragmentation peaks, m/z 205 (C13H17O2) and m/z 203 (C13H15O2) are formed after the loss of the phytyl chain. The (3-, y-, and 5-tocotiienols show corresponding M+ peaks at 410, 410, and 396, respectively. 

MarceUomycine behaves similarly and, as for vitamin Ki, these processes are attenuated in acidic media. They have been attributed to the long side chain fixed on the quinonic structure the phytyl chain in the third position for vitamin Ki and the daunosamine sugar moiety in the seventh position for marcellomycine. 

Comparing the slopes of both vitamins Ki and K3, it appears that the adsorption method is about ten times more sensitive for the latter compound. This could be attributed to the phytyl chain in vitamin Ki which increases the size of the molecule. However, marcellomycine exhibits sensitivities comparable to those of vitamin K3. This may be explained by a favourable orientation of the daunosamine moiety of marcellomycine while the longer phytyl chain of vitamin Ki leads to a steric hindrance. 

FIGURE 14.4 Dimer of chlorophyll (phytyl chains not shown). The shape of the dimer is due to the charges of opposite signs coming closer hy skewing the two planes. The most important attraction is between the carboxyl group at the upper left of the lower monomer and the Mg ion at the center of the upper monomer. 

Both quinones are provided with an isoprenoid chain, which very likely functions biologically as an anchor of the molecule to the protein. In the same way, BChl and Chi molecules appear to be anchored by the phytyl chain. All four BChl molecules are attached to the molecule by an axial ligand, binding to the... 

Vitamin Ki is best synthesized by condensation of a menadiol 1-ester with phytol or isophytol and subsequent saponification and oxidation. Vitamin Ki synthesized from phytol appears to be identical with the natural product vitamin Ki from synthetic isophytol differs slightly in having a racemic phytyl chain. The double bonds in /3,7-position of all vitamin K compounds have the same, most probably the irons, configuration. 

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