Phosphates cleaved

As shown in Scheme 1, two other pathways lead to the formation of dolichol phosphate. These are (a) phosphorylation of the free poly-prenol, and (b) dephosphorylation of dolichol diphosphate. A dolichol phosphate-cleaving phosphatase has been described as occurring in Tetrahymena pyriformis,15 human lymphocytes,18 calf brain,17 and rat-nerve tissue.18 The protozoal enzyme was a soluble acid phosphatase, although it was clearly different from the bulk phosphatase activity, whereas the mammalian enzymes had optima at neutral pH and were membrane-bound. 

Remove protecting groups from bases Remove cyanoethyl groups from phosphates Cleave chain from silica support... 

Moore and Trego described the use of triphenyl phosphine and di-A/-butyl phosphate as chemical probes to establish a cross-link network structure in rubber vulcanizates. " Triphenyl phosphine and trialkyl phosphates cleave di- and polysulfide, as illustrated in Fig. 4. 

In contrast to DNA, RNA is sensitive to hydrolysis, even at pH 7.0. The reason is that the 2 OH group, which DNA lacks, can attack the 3 phosphate, cleaving the RNA backbone... 

Zigmond, 1988). The ATP-hydrolysis that accompanies actin polymerization, ATP —> ADP + Pj, and the subsequent release of the cleaved phosphate (Pj) are believed to act as a clock (Pollard et ah, 1992 Allen et ah, 1996), altering in a time-dependent manner the mechanical properties of the filament and its propensity to depolymerize. Molecular dynamics simulations suggested a so-called back door mechanism for the hydrolysis reaction ATP ADP - - Pj in which ATP enters the actin from one side, ADP leaves from the same side, but Pj leaves from the opposite side, the back door (Wriggers and Schulten, 1997b). This hypothesis can explain the effect of the toxin phalloidin which blocks the exit of the putative back door pathway and, thereby, delays Pi release as observed experimentally (Dancker and Hess, 1990). 

An example of a biologically important aide hyde is pyridoxal phosphate which is the active form of vitamin Bg and a coenzyme for many of the reac tions of a ammo acids In these reactions the ammo acid binds to the coenzyme by reacting with it to form an imine of the kind shown in the equation Re actions then take place at the ammo acid portion of the imine modifying the ammo acid In the last step enzyme catalyzed hydrolysis cleaves the imme to pyridoxal and the modified ammo acid... 

Following Its formation D fructose 6 phosphate is converted to its corresponding 1 6 phosphate diester which is then cleaved to two 3 carbon fragments under the mflu ence of the enzyme aldolase... 

Rapid inactivation of added lincomycin was found to result from the growth of Streptomjces rochei in a synthetic medium the antibiotic was converted into lincomycin 3-phosphate [23670-99-7] (5, R = CH3, R = PO3H2, R = SCH3), C2gH33N202PS, readily cleaved back to the antibiotic upon treating with alkaline phosphatase (53). 

To cleave p-methoxyphenylmethyl (MPM) ethers DDQ (dichlorodicy-anobenzoquinone)//-BuOH-CH2Cl2 phosphate buffer (pH 7.0), 4.5 h. 

A variety of cyclic ortho esters,including cyclic orthoformates, have been developed to protect czs-1,2-diols. Cyclic ortho esters are more readily cleaved by acidic hydrolysis (e.g., by a phosphate buffer, pH 4.5-7.5, or by 0.005-0.05 M HCl) than are acetonides. Careful hydrolysis or reduction can be used to prepare selectively monoprotected diol derivatives. 

The SEM ester was used to protect a carboxyl group where DCC-mediated esterification caused destruction of the substrate. It was formed from the acid and SEM chloride (THF, 0°, 80% yield) and was removed solvolytically. The ease of removal in this case was attributed to anchimeric assistance by the phosphate group. Normally SEM groups are cleaved by treatment with fluoride ion. Note that in this case the SEM group is removed considerably faster than the phenyl groups from the phosphate. ... 

FIGURE 4.30 Calibration curves for double-stranded DNA fragments on TSK-GEL SW and TSK-GEL PW columns. Column TSK-GEL SW or TSK-GEL PW, two 7.5 mm X 60 cm columns in series. Sample 22 fragments from Hoelll-cleaved pBR322 DNA and 6 fragments from EcoRI-cleaved pBR322 DNA. Elution 0.1 M NaCI in 0.1 M phosphate buffer, pH 7.0, plus I mM EDTA Flow rate 1.0 ml/min. Detection UV at 260 nm. 

FIGURE 7.23 The starch phosphorylase reaction cleaves glucose residues from amy-lose, producing a-D-glucose-l-phosphate. 

The base-specific chemical cleavage (or Maxam-Gilbert) method starts with a single-stranded DNA that is labeled at one end with radioactive (Double-stranded DNA can be used if only one strand is labeled at only one of its ends.) The DNA strand is then randomly cleaved by reactions that specifically fragment its sugar-phosphate backbone only where certain bases have been chemically removed. There is no unique reaction for each of the four bases. However,... 

Subsequent action by fructose-l-phosphate aldolase cleaves fructose-l-P in a manner like the fructose bisphosphate aldolase reaction to produce dihy-droxyacetone phosphate and D-glyceraldehyde ... 

The related [(3,4-dimethoxybenzyl)oxy]methyl group has been used similarly, except that, as expected, it is more easily cleaved (DDQ, CH2CI2, t-BuOH, phosphate buffer, pH 6.0, 23°, 110 min, 88% yield). ... 

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