Phosphates modification

Traditional methods to map posttranslational modification sites, like those of phosphorylation, have been anchored by protein digest and mass spectroscopic (MS) approaches (for a review on the classic evaluation and for MS analyses of O-glycans, see Reference (56)). Unfortunately, like many posttranslational modifications, O-GlcNAcylation occurs routinely on a protein population with substoichiometric frequency, which results in a very small detectable population of a O-GlcNAc-modified product. Also, much like O-phosphate additions, the protein-O-GlcNAc bond is labile and is detached by collision-induced dissociation (CID) during MS analysis. Often, the bond is lost before it can be detected on the peptides analyzed (57, 58). Phosphate modifications, however, can overcome this limitation by emiching the peptide mixtures... 

Several uimatural nucleoside phosphate modifications (Fig. 2e) have been generated, which include phosphorothioate, phosphoroamidate, phosphorothiolate, and methylphosphonate derivatives. The syntheses of these modifications have been reviewed by Verma and Eckstein (19). A modification of those procedures can be used for the generation of phosphoroselenoate RNAs (20). 

Interaction with the matrix (untreated calcium carbonate in PE decreases tensile strength but after phosphate modification tensile strength is increased glass beads may decrease or increase tensile strength depending on their interfacial adhesion mica and talc give a similar effect in PP polyamide fiber does not reinforce natural rubber because of its lack of interaction)... 

Kanistanon D, Powell DA, Hajjar AM et al (2012) Role of Francisella lipid A phosphate modification in virulence and long-term protective immune responses. Infect Immim 80 943-951... 

Phosphate modifications T7 polymerase does not discriminate significantly between NTP and [aS] NTP (NEN). To obtain the appropriate modification level the NTP is substituted with [aS] NTP to the desired level. A standard transcription protocol, such as the one described in Section 2.3.1, can be used. 

Concurrent base and phosphate modification The current examples of cotranscriptional incorporation of modified bases are rather limited,14-16 and the modified NTPs are generally not commercially available. The standard buffer conditions can be employed, but the modified nucleotides are incorporated with different efficiencies e.g. 5% incorporation of inosine at the G positions requires 40% inosinetriphosphates in the reaction mixture, while 7-methyl-guano-sine is incorporated as readily as GTP. 

Fig. 4.16. Autoradiograms showing a chemical interference analysis of RNA using base modifications (A), or phosphate modifications (B). A 37-nucleotide long RNA...

The location of the two pyridoxal phosphate modification sites is of obvious interest, since they provide a marker for the reductase binding site. In the preliminary report 218), three pyridoxal phosphate-containing peptides were found residues 1-10, 68-74, and 83-94. Candidates for modification therefore include lysines 5, 7, 8, 86, 87, and 88 at the top of the molecule, and 72 and 73 on the left side. The further narrowing down of these groups will be awaited with great interest. 

Protein semisynthesis and, in particular, EPL can provide a straightforward route to phosphonate incorporation. Indeed, these techniques prove valuable for site-specific incorporation of the standard phosphoamino acids which have been effectively used in structural and enzymatic analyses [9, 23]. EPL is most efficiently used when the phosphate modification is within 50 amino acids of... 

The ability to synthesise oligonucleotides containing modified phosphodiester linkages continues to be of great interest in the therapeutic area. In particular it is desirable to confer through these modifications enhanced cell permeability properties and nuclease resistance. Several previous candidates that confer these properties have modified the pho,sphodiester linkage in such a way that creates a chiral centre at phosphorus. The resultant complex mixture of diastereoisomers all meet the above requirements to different extents, Over the past year efforts have therefore concentrated on the synthesis of achiral alternative linkages or stereospecific syntheses of chiral phosphate modifications. A number of literature summaries in this area have appeared recently. 

Figure 27 Illustration of the bioswitch process Bioconjugate with suppressed aggregation tendency by 0-phosphate modifications of the threonine residues (a) enzymatic cleavage of the phosphates activates the self-assembly tendency of the peptide (b) and peptide-guided microstructure formation, leading to fibrillar core-shell tapes (c). Adapted from ref 442.

The Lewis acid of zirconia can be blocked by other than fluoride. The effectiveness of the blocking of the Lewis acid sites should be related to the strength of the interaction between the Lewis base used and the zirconium ion coordination site. Blackwell and Carr have developed the relative eluotropic strength of a number of Lewis bases in terms of their ability to elute a wide variety of benzoic acid derivatives. Phosphate ranks at the top of the elution series. It brought about elution of the benzoic acid derivatives in the column dead volume. This proves that phosphate binds strongly to the surface of zirconia. The strong affinity of zirconia for phosphate suggested that a phosphate modification of the surface should be a reasonable approach. 

Schafer et al. used several spectroscopic techniques to characterize the surface species on phosphate-modified zirconia particles. Their results show that phosphate merely adsorbs on the surface of zirconia under the mildest phosphate concentration, i.e., neutral pH, room temperature, and short contact times. However, at acidic pH and higher temperarnres, esterification of the phosphate with surface hydroxyls takes place as the kinetic barriers are overcome. The solid NMR studies clearly show the presence of covalently bound phosphate. This phosphate modification effectively blocks the sites responsible for the strong interaction of certain Lewis bases with the zirconia surface, resulting in a more biocompatible stationary phase. Unlike fluoride-modified zirconia, phosphate-modified zirconia behaves as a classic cation exchanger and not as a mixed-mode medium analogous to hydroxyapatite, despite spectroscopic evidence of zirconium phosphate formation on the surface. This limits the applicability of the supports, as most proteins and enzymes are anionic at neutral pH. Nevertheless, its ability to separate proteins with high p/ values still deserves much attention. The preparative-scale separation of murine IgGs from a fermentation broth demonstrates the utiUty of the supports for solutes that are retained. 

Korosi L, Oszko A, Galbacs G, Richardt A, Zollmer V, Dekany 1 (2(X)7b) Structuial properties and photocatalytic behaviour of phosphate-modified nanocrystalline titania films. Appl Catal B 77 175-183 Korosi L, Papp S, Beke S, Oszko A, Dekany I (2010) Effects of phosphate modification on the structure and surface properties of ordered mesoporous SnOj. Micropor Mesopor Mater 134 79-86 Korotcenkov G (2005) Gas response control through structural and chemical modification of meted oxides state of the art and approaches. Sens Actuators B Chem 107 209-232... 

Thermodynamic and kinetic data snggest that quadruplex stability depends on a nnmber of factors, including the type of structure adopted by the DNA strand (or strands), strand sequence, the size of intervening loops, base and phosphate modifications, pH and the presence of cations [19]. Small molecules may stabilize quadraplex DNA (or facihtate DNA folding into quadruplex structures) due to shifting the competitive equilibrium between the single-stranded or Watson-Crick duplex and quadruplex DNA towards the latter form [19,20]. Inhibition activity of G4 ligands depends mainly on the stability of their complexes with telomeric DNA quadruplexes. 

Chem. Descrip. Cocamide DEA, DEA 2-ethylhexyl phosphate salt, DEA (15%), phosphate-modifed Ionic Nature Anionic... 

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