Ribose conjugates

Since artifacts may be formed in the course of labeling experiments with permeabilized cells, the ADP-ribosylated proteins of the nuclear matrix were identified by another experimental approach. After labeling of cellular proteins by 24 h incubation with [ S]-methionine, the matrix was isolated from the intact cells. In subsequent chromatography, the ADP-ribosylated proteins were selectively isolated due to the binding of the cis-diol grouping within the sugar component of the ADP-ribose conjugates onto the boronate column. While only 2% of the total matrix proteins were bound, control... 

The present study represents an attempt to characterize the proteins undergoing poly-(ADP-ribose) modification in association with myogenesis. Although we have not yet performed analysis of poly(ADP-ribose) conjugates of histones which are the main acceptors in many systems [20, 21], several interesting observations have emerged from our study. 

The aryl azido derivatives of [32P]NAD+ were employed to site-specifically incorporate photoactivatable ADP-riboses to transducin at Cys-347 by means of pertussis toxin, and the conjugation was followed by irradiation. Photocrosslinking revealed three major bands after irradiation which corresponded to a-y(47 kDa), a-a (83 kDa),and a-a-a (105kDa) subunit contact domains [88]. 

Besides 0-glucuronides, a number of other O-glycosides are potential substrates for hydrolysis mediated by glycosidases (EC 3.2.1). These xeno-biotics, and, in a few cases, metabolites thereof, include conjugates of glucose (glucosides), rhamnose (rhamnosides), ribose (ribosides), and many others. 

Nucleoproteins, which are conjugated proteins, may be separated into nucleic acids and proteins. The name nuclein, which was coined by Miescher in 1869 to describe products isolated from nuclei in pus, was later changed to nucleic acid. Somewhat pure nucleic acid was isolated by Levene in the first decade of the 20th century. He showed that either o-ribose or D-deoxyribose (Figure 10.7) was present in what are now known as RNA and DNA. 

Nucleotides are the phosphoric acid ester of nucleoside, while nucleosides are compounds in which nitrogenous bases (purines and pyrimidines) are conjugated to the pentose sugar (ribose or deoxyribose) by a b-glycosidic linkage. AMP, ATP, ADP, GMP, CMP, UMP are the examples of mononucleotides. 

Fig. 29. Structure of a variety of labeled nucleotides. A biotin-labeled UTP B Gamma labeled 32P-ATP C The ribose-modified fluorescent ATP analogue, -EDA-ATP, which was synthesized by conjugating Cy3 reactive dye with 2 (3 )-0-[iV-(2-aminoethyl)carbamoyl] ATP (EDA-ATP).

The perchlorates of various secondary amines, such as diphenylamine and indole derivatives, are colorless.64 The similarity of colors produced in the presence of hydrochloric acid also attests to the non-auxochromic character of the perchlorate ion in the production of the colored derivative. Consequently, the only role attributable to the perchloric acid in this test is that with nucleic acids it leads to more effective hydrolysis and releases more 2-desoxyribose for reaction with tryptophan. This reaction leads to the production of a substance of the type represented by XV and XVI (R " = H), and the increase in the number of conjugated double bonds results in the product being colored. With ribose, which has a free hydroxyl group at carbon atom 2, a ketone of the type shown in XVII can be formed, and in this case the net result is no increase in the number of double bonds conjugated with the indole nucleus and no comparable increase in color. Hence the test will distinguish between ribose and 2-desoxyribose. 

Because the geometry of the 9-double bond was not clear at that time, Corey et al. 75> tried to prepare the (Z)-9-isomer as well as the ( )-9-isomer of leukotriene-A (78 and 86). In the synthesis of the former isomer the tribenzoyl derivative of D-(—)-ribose (79) was converted in 8 stepy into the optically active epoxyaldehyde 71 and the latter to 72. 72 was olefmated with ylide 82, generated by treatment of the corresponding phosphonium mesylate with lithium diisopropylamide in THF/ HMPA75) (Scheme 15). In the first olefination step 72+82- 78, however, similar to the first method, a A9-isomer mixture was formed. The loss of (Z)-selectivity of the Wittig reaction is due to the use of conjugated unsaturated, i.e. moderate ylides of type 82, and had to be expected because of the mechanism of the Wittig reaction (see Sect. 2). 

The tandem Wittig-conjugate-addition reaction shown below has found widespread application for the synthesis of C-nucleosides from aldoses, in most cases ribose (see also Section 4.7.1.2.2. for the related reaction of aldoses with nitroalkanes). 

Cervantes-Laurean, D., Jacobson, E. L., and Jacobson, M. K. (1997), Preparationof low-mo-lecular-weight model conjugates for ADP-ribose linkages to protein. MctJrftfs Enziprsot. 280, 275-287. 

Less commonly, conjugation with other sugars such as glucose, ribose or xylose can occur, and for example, glucosides are formed following conjugation with UDP-glucose. 

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