Synthesis of PS

The regulation of the appearance of the 66 kDa polypeptides may take place at a post-transcriptional step. In maize, transcripts of the two genes, psaA and psaB, are present in dark-grown plants [90], and therefore, if maize does not accumulate 66 kDa polypeptides in the dark, there must be some mechanism to prevent translation of the mRNA or to degrade newly synthesized polypeptides. There is no information on the transcripts for other polypeptides of PS I in dark-grown plants. 

The sites of synthesis of the smaller polypeptides of the core complex are not clearly established. Several methods, including the use of specific inhibitors of protein synthesis and synthesis in isolated chloroplasts, have suggested that two of the polypeptides are synthesized on chloroplast ribosomes. Experiments examining the effect of chloramphenicol and cycloheximide on the labelling of PS I polypeptides have suggested that in Spirodela two polypeptides of 12 and 8 kDa are synthesized on chloroplast ribosomes [121], whereas in pea a polypeptide of about 6 kDa was labelled in the presence of cycloheximide but not chloramphenicol [136]. In both plants the 66 kDa polypeptides were synthesized in the presence of cycloheximide but not chloramphenicol, indicating their synthesis on chloroplast ribosomes [121,136]. Incorporation of labelled amino acids into PS I polypeptides in isolated chloroplasts has indicated that one or two polypeptides, in addition to the 66 kDa polypeptides [137], are synthesized on chloroplast ribosomes. In pea chloroplasts polypeptides of 15 kDa [136] and 17 and 11 kDa [138] have been reported to be labelled, and in wheat a polypeptide of 15 kDa has been reported to be labelled in isolated etiochloroplasts [139]. The different electrophoresis systems used preclude any direct comparison of the sizes of these polypeptides, but the conclusion must be that two, or more, of the smaller polypeptides of the PS I complex are synthesized on chloroplast ribosomes. 

Further study is needed to define the polypeptide composition of PS I and in particular to identify equivalent polypeptides in PS I preparations from different plants. Only then will it be possible to compare results from different laboratories and produce a comprehensive view of the synthesis of PS I in higher plants. 

Chloroplast ATP synthase is a well-defined complex which may be solubilized fi om thylakoid membranes by treatment with octylglucoside and cholate and purified by ammonium sulphate fi actionation and sucrose density gradient centrifugation [140]. The complex is composed of two assemblies of polypeptides CFj, a peripheral membrane complex, which may be washed fi-om thylakoid membranes with EDTA and which shows latent ATPase activity, and CFg, the intrinsic membrane sector, which translocates protons across the thylakoid membrane. 

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The above methods occurred in 3 steps, therefore, these methods are not preferred. For instance, in the first step, o-, m-, and p-bromostyrene and its copolymer are synthesized. In the second step, Li-PS is synthesized from the reaction of copolymers with an organic compound containing LI. The abovementioned reactions are made with different compounds of Li-PS in the third step. These methods were also investigated by Ayres and Mann [34], who used the synthesis of PS containing chloro groups with chloromethylated PS as the first step. In the second step, formil resin was obtained by oxidation of chlorometylated PS. In the third step, carboxyl-ated PS was obtained by the oxidation of formol resin with acetic acid at 20°C for 48 h. There are some disad-... 

As shown for the synthesis of PS [291], the monomer may be localized in the vicinity of the filler surface by previously grafting a polymer capable of swelling in the base monomer. Copolymeric latex of polychloroprenemethacrylic acid was added to the aqueous dispersion of chalk. The acid groups reacted with chalk and the latex particles became chemically grafted to chalk. When further portions of styrene were added they were completely absorbed by modified chalk. 

By utilizing a combination of RAFT and cationic ROP, the synthesis of [poly(methyl methacrylate)][poly(l,3-dioxepane)][polystyrene] miktoarm star terpolymers was achieved [182], The approach involved the synthesis of PS functionalized with a dithiobenzoate group by RAFT polymerization and subsequent reaction with hydroxyethylene cinnamate (Scheme 98). The newly created hydroxyl group was then used for the cationic ring opening polymerization of 1,3-dioxepane (DOP). The remaining dithiobenzoate group was used for the RAFT polymerization of methyl methacrylate. 

Fig. 9.31 a) Synthesis of PS-b-polyacrylate brushes by LCSIP and consecutive ATRSIP [282]. AFM images of the tethered PS-fa-PMMA brushes with 23 nm thick PS layer and 14 nm thick PMMA layer b) after treatment with CH2CI2, c) with cyclohexane and d) after solvent exchange from CHjClj to cyclohexane, e) Cartoon proposing a model for the regular nanopattern morphology ( pinned micelles )... 

The synthesis of PS chiral analogues of biophosphates via P compounds required as therapeutic continues to attract attention. It is apparent that future perspectives in this fascinating area will focus on finding easy access to chiral P compounds other than the separation of diastereoisomers and improvements in the stereoselective coupling procedures. So far research efforts in synthesis of new drugs with a phosphorus backbone has paid insufficient attention to cost and difficulties of large scale production [110]. This chapter illustrated the trends with a series of selected examples. 

The primary pathway for synthesis of PS in mammalian tissues is provided by the base exchange reaction, in which the ethanolamins of PE is exchanged for free serine (see Figure 17.6). This reaction although reversible, is used primarily to produce the PS required for membrane synthesis. 

A similar synthetic route was adopted by Stadler et al. for the synthesis of (PS)(PB)(PMMA) stars [54] as shown in Scheme 21. Living PS chains were end-capped with l-(4-bromomethylphenyl)-l-phenyl ethylene to produce the macromonomer. The capping reaction with DPE was employed in order to reduce the reactivity of the PSLi chain ends thus avoiding several side reactions (trans-metallation, addition to the double bond of the DPE derivative). The next step involved the linking of living PB chains, prepared in THF at -10 °C to the end double bond of the macromonomer. This produces a new active center which was used to initiate the polymerization of MMA leading to the formation of the desired product. 

SCHEME 14.14 Synthesis of PS A1 repeating tetrasaccharide unit from Bacteroides fragilis by Seeberger and coworkers. DMTST, dimethyl(methylthio)sulfonium triflate TTBP, 2,4,6-tri-terf-butylpyrimidine. 

Consistently, Anderson and coworkers showed that the polymerization of MMA in THF at —78 °C is living when initiated by DPHLi (10), which is nothing but the model of the diphenylalkyl anion (9) of the PS macroinitiator used in the synthesis of PS-fcZock-PMMA (equation 21). It must be noted that DPHLi (10) results from the direct addition of DPE (8) to n-Buli (equation 22)". The molecular weight of PMMA is predetermined by the monomer-to-initiator molar ratio and the MMA conversion. The polydispersity index is low (1.04 < Mw/Mn < 1.16). The livingness of this polymerization was confirmed by the successful resumption of the polymerization of lauryl methacrylate (LMA), and formation of the parent PMMA-fc/ock-PLMA diblocks. The anionic polymerization of MMA in THF at —78°C is thus living , provided that sterically hindered initiators are used. 

For the preparation of optically active P-lactams (154) with relative trans configuration (e.g. for the synthesis of (+)-PS-5 ), the [2 -i- 2] cycloaddition of ester enolates such as (152) and A -trialkylsilyl-imines (153) is an appropriate strategy (Scheme 70).In this case, chirality is introduced by the imino moiety. 

The early attempts to use relatively easily available diastereomerically pure nucleoside 3 -0-(2-cyanoethyl-AT,AT-diisopropylphosphoramidite) monomers for the stereospecific synthesis of PS-Oligos failed because of inevitable racemiza-tion of Pm intermediate caused by an excess of lff-tetrazole necessary for efficient elongation of oligonucleotide chain [13]. An idea to use for that purpose appropriately protected nucleosides functionalized at 3 -0 position with 2-thio-1,3,2-oxathiaphospholane moiety arose from the studies on the reactions of di-substituted phosphorothioates with oxiranes [14,15], and in particular from the observation that PS-PO exchange in 0,0-diphenyl phosphorothioate (8) upon treatment with ethylene oxide in methanol solution resulted in formation of... 

Table 1. Synthetic protocol for the 1 -pmol scale automated solid-phase synthesis of PS-oligos using monomers 15, or PO-oligos using 17...

To avoid the P-elimination-promoted rearrangements observed when the promising indolooxazaphosphorine approach was applied to solid phase synthesis of PS-oligos, Just developed a set of chiral auxiliaries, derived from d- and L-tryptophan, that could be removed by direct displacement of the primary... 

Almost the same method was used in another study for the synthesis of PS-g-PEO graft copolymers [80]. These results suggest the existence of narrow molecular weight distribution branches attached to a rather polydisperse backbone. 

The synthesis of PS and transport to the mitochondria have been successfully reconstituted using permeabilized cells [25]. The transport of PS to the mitochondria in per-meabilized mammalian cells occurs in the absence of cytosol, displays an absolute requirement for ATP, and occurs with a t,/2 of approximately 3 h at 37°C. This transport does not require ongoing synthesis of PS, and 45-fold dilution of the permeabilized cells does not alter the rate or extent of transport. These results are consistent with a membrane-bound transport intermediate that utilizes zones of close membrane apposition between the ER and the mitochondria. Although there is no absolute requirement for cytosol in the transport reaction, a soluble 9-kDa Ca -binding protein, named SIOOB, that is highly conserved across mammalian species can enhance the transport several fold (O. Kuge, 2001). Permeabilized yeast have also been used to examine PS transport (G. Achleitner, 1995). Unlike mammalian cells, the transport of PS to yeast mitochondria does not require ATP. 

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