Reconstitutive Condensation

The intermolecular variant of the O-H insertion reaction gets stuck at the stage of the initial adduct 8. We envisioned that if R1 = allyl, coordination of the double bond to the metal would initiate a Claisen-type process to form the jr-allylruthenium complex 9, whose reductive elimination would form the allyl ketone starting from terminal alkynes and allyl alcohols (Equation 1.10). Gratifyingly, this prediction was fully realized as shown in Equation 1.11 [13]. A tertiary ester does not undergo elimination under these reaction conditions (Equation 1.12). Dihydroxylationofthe double bond and subsequent acidification effect cyclodehydration to form furans in two overall steps. Subsequent elimination of the elements of acetic acid completes a synthesis of rosefuran 10, one of the most prized fragrances [14]. 

With terminal alkynes bearing propargylic alcohols, formation of the vinylidene is complicated by the competitive formation of the allenylidene as shown in Equation 1.13. 

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The preparation of optically active ruthenium vinylidene complexes to perform asymmetric reconstitutive condensation has been carried out with moderate enantioselectivities [38,39]. 

If sweetened condensed milk is not used then milk powder is the most likely alternative. In some cases, milk powder is added to sugar and water to produce a reconstituted condensed milk. One simple reason for doing this is that the plant could have been constructed to use condensed milk. 

In the case of a substrate bearing a second hydroxyl group, the aHenylidene can undergo nucleophilic attack at the y-carbon to re-form a vinylidene [15]. In such an event, the newly formed vinylidene can then undergo the reconstitutive condensation shown in Equation 1.14 [16]. This reaction provides access to the spiroketal of calyculin A, a nanomolar inhibitor of serine/threonine phosphatases. 

Trost, B.M., Dyker, G. and Kulawiec, R.J. (1990) A ruthenium-catalyzed reconstitutive condensation of acetylenes and allyl alcohols. Journal of the American Chemical Society, 112, 7809-7811 Trost, B.M. and Kulawiec, R.J. (1992) Mechanism of the ruthenium-catalyzed reconstitutive condensation of allylic alcohols and terminal alkynes. Journal of the American Chemical Society, 114, 5579-5584 Trost, B.M., Kulawiec, R.J. and Hammes, A. (1993) Ruthenium catalyzed reconstitutive condensation. Application to functionalized steroid side chains. Tetrahedron Letters, 34, 587-590. 

The residue is reconstituted to 1 inL in pentane-diethyl ether (19 1, v/v). This fraction is loaded on to a 15-cm bed of Florisil previously capped with 1 cm of anhydrous sodium sulfate and with pre-wetting of the column bed with pentane-diethyl ether (19 1, v/v). The vessel with the previously reconstituted fraction is rinsed twice each time with 1 mL of pentane-diethyl ether (19 1, v/v) and the rinsates are added to the Florisil column. The column is washed with lOmL of pentane-diethyl ether (19 1, v/v) and this fraction is discarded. The analyte is eluted with 25 mL of pentane-diethyl ether (19 1, v/v) and the eluate is collected in a K-D evaporator. A Vigreaux condenser is fitted and the organic fraction is evaporated to near dryness (the last traces of diethyl ether and pentane are removed using a gentle stream of dry nitrogen gas). The residue is reconstituted to 5 mL using toluene. 

Mg (but not Na" ") results in a structure that is equivalent to the 30-nm compact fiber in the extent of condensation [49]. Finally, the independent and critical function of core histone N-termini in chromatin condensation was demonstrated by showing that nucleosomal filaments reconstituted from core histones lacking their N-terminal domains are unable to condense into folded structures upon an increase of Mg " ", despite the presence of properly bound histone H5 ([50,51], see also Ref. [52] for the discussion of the special role of H3 and H4 tails). Thus, the presence of HI is not a sine-qua-non condition for salt-induced chromatin folding, which can proceed in Hi s absence and is an intrinsic property of filaments consisting of spaced core particles. A key question is how many of the features of the native 30-nm compact fiber are due to the presence of histone HI From the available data it seems that HI may influence the intrinsic folding pathway of the chromatin filament by stabilizing a single ordered conformation. This property can have much to do with the cooperativity of HI interactions within chromatin but also with the way HI is bound to the nucleosome and with the efifect it exerts on the path of linker DNA. 

Studies with native and reconstituted chromatin show that phosphorylated HI destabilize chromatin structure [62,63]. Phosphorylation of HI increases the protein s mobility in the nucleus and weakens its interaction with chromatin [64,65]. In studies with avian fibroblasts transfected with H5 (an HI variant), H5 was shown to inhibit proliferation in normal fibroblasts but not in transformed cells, in which H5 was phosphorylated. Aubert et al. proposed that phosphorylated H5 lacked the ability to condense chromatin [66]. The greater affinity of the dephosphorylated relative to phosphorylated HI for chromatin may interfere with the performance of chromatin remodeling agents. For example, dephosphorylated, but not phosphorylated, HI inhibited chromatin remodeling by SWI/SNF [67]. Thus, these and other studies provide support for the idea that an increase in the phosphorylation of HI leads to destabilization of the chromatin [24]. 

Heat is reconstituted in each star. Condensing and heating up the matter within them, stars are the antithesis of the Big Bang, making up for the nuclear... 

Principal micelle characteristics. The structure of the casein micelles has attracted the attention of scientists for a considerable time. Knowledge of micelle structure is important because the stability and behaviour of the micelles are central to many dairy processing operations, e.g. cheese manufacture, stability of sterilized, sweetened-condensed and reconstituted milks and frozen products. Without knowledge of the structure and properties of the casein micelle, attempts to solve many technological problems faced by the dairy industry will be empirical and not generally applicable. From the academic viewpoint, the casein micelle presents an interesting and complex problem in protein quaternary structure. 

Fig. 13 (a) Three enzymes (EntE, EntB and EntF) are required for the in vitro reconstitution of 64. (b) Biosynthesis of 64 by the stepwise condensation of three ArCP-bound DHB groups (79) and three PCP-bound L-serines (80a). Enterobactin (64) chelates ferric iron with high affinity via the six phenolate hydroxyl groups... 

Although the amino acid sequence as well as the secondary structure of fibroin differs from those of spidroin, the fibers spun from these proteins, that is, silkworm silk and spider silk have comparable mechanical properties. These may be attributed to the structural characteristics, both at the molecular and filament level. The superior mechanical properties of silk-based materials, such as films, coatings, scaffolds, and fibers produced using reconstituted or recombinant silk proteins, are determined by their condensed structures. 

The biosynthetic pathway is outlined in Figure 1. The thiazole 4 is formed by an oxidative condensation of glycine (1), deoxy-D-xylulose-5-phosphate (DXP, 2), and a sulfide carrier protein with a thiocarboxylate at its carboxy terminus (ThiS-COSH, 3). The pyrimidine phosphate 8 is formed by a deep-seated rearrangement of aminoimidazole ribotide (AIR, 7). It is then pyrophosphorylated and used to alkylate the thiazole to give 10. A final phosphorylation completes the biosynthesis. The entire pathway from glycine, DXP, cysteine, AIR, and ATP has now been reconstituted using purified enzymes. 

The silicatein a subunit alone proved sufficient to catalyze the acceleration of TEOS condensation at neutral pH [7], For these experiments, we purified and reconstituted the silicatein a subunit that we produced from a recombinant DNA that we cloned in bacteria — cells which normally would make no silicatein without the introduced recombinant DNA template (Fig. 5). This method allowed us to be sure that the catalysis of silica synthesis we observed was due solely to the silicatein a protein produced from the cloned DNA and purified from the bacteria, since no other proteins from the sponge could be present. 

In attempts to reconstitute nucleosomes on SV40 circular DNA, Cap-lan et al. (37) observed that if the histones were ADP-rihosylated prior to reconstitution assembly of nucleosomes was inhibited by as much as 80%. If nucleosomes were first allowed to assemble, then modified by ADP-ribosylation, no eflPect on stability was observed. These data led the authors to speculate that ADP-ribosylation of histones prior to nucleosome assembly might be of physiological importance. Perella and Lea (168, 169) have shown that in rat liver nuclei, polyamines cause an increase in histone Hi ADP-ribosylation and histone HI dimer synthesis, which is accompanied by a decrease in core histone ADP-ribosylation. Data such as these have led to speculation that Hi dimer formation may function in the condensation or stabilization of chromatin fibers (35, 119). The data of Lorimer et al. (124) indicate that dimer synthesis is inversely related to the nuclear activity of the poly(ADP-ribose) glycohydrolase. Thus, these authors (124) inferred that the Hl-Hl-polymer complex formation is of a transient nature. As pointed out by Purnell et al. (171), if this crosslink were to function in the stabilization of chromatin, the modified histone Hi would have... 

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