Ribose moiety

Phosphate esters of glucose, fructose, and other monosaccharides are important metabolic intermediates, and the ribose moiety of nucleotides such as ATP and GTP is phosphorylated at the 5 -position (Figure 7.13). 

Pertussis toxin is produced by the bacterium Bordetella pertussis. It covalently modifies G-proteins of the G/Go family (transfer of a ADP-ribose moiety of NAD onto G-protein a-subunits). ADP-ribosylated G-proteins are arrested in their inactive state and, as a consequence, functionally uncoupled from their respective effectors. Examples for pertussis toxin-sensitive cellular responses include the hormonal inhibition of adenylyl cyclases, stimulation ofK+ channels, inhibition of Ca2+ channels and stimulation ofthe cGMP-phosphodiesterase in retinal rods. 

With the same synthetic sequence, labeled ribose molecules produced AIRs labeled on the ribose moiety. From D-erythrose and (l3C)NaCN, the Fischer-Kiliani synthesis, as modernized by Serianni et al.59 produced D-(l-l3C)ribose and D-(l-l3C)arabinose. The labeled arabinose was transformed into D-(2-l3C)ri-bose in the presence of dioxobis(2,4-pentanedionato)-0-0 -molybdenum(VI) in... 

After silylation-amination in situ transsilylation (cf Section 2.3) of the intermediate persilylated cytidines 5 with excess boiling methanol for 3-5 h gives the desired free cytidines 6 and methoxytrimethylsilane 13a (b.p. 57°C) [13]. Thus protection of the alcohohc hydroxyl groups of the ribose moiety and silylation-activation of the 4-position in the pyrimidine moiety in persilylated uridine 3, and the concomitant amination of 3, aU in one reaction step, to 5 is followed finally by in situ transsilylation (cf. Section 2.3) with excess boihng methanol in one reaction vessel. 

O-acetylation of the aliphatic hydroxyl groups of the ribose moiety (or other sugar moieties) to the 2, 3, 5 -tri-0-acetates ... 

Ribonucleotide reductase differs from the other 5 -deoxyadenosyl-cobalamin requiring enzymes in a number of respects. Hydrogen is transferred from coenzyme to the C2-position of the ribose moiety without inversion of configuration. Also since lipoic acid functions in hydrogen transfer, exchange with solvent protons takes place. Furthermore, exchange between free and bound 5 -deoxyadenosylcobalamin occurs rapidly during catalysis. Evidence for a Co(I)-corrin as an intermediate for this reduction is presented in our section on electron spin resonance. 

The pH dependence of the reaction of m-tolyl acetate with cyclohexa-amylose implies a pAa of 12.1 for the catalytically active secondary hydroxyl group (Van Etten et al., 1967b). Although this pK at first appears low for the ionization of an aliphatic alcohol, it is consistent with the value of 12.35 determined thermodynamically for the ionization of the secondary hydroxyl groups of the ribose moiety of adenosine (Izatt et al., 1966 Christensen et al., 1966), and with the value of 12.2 reported by Lach for the... 

In studies on new bicyclic nucleosides the derivative 57 containing a ribose moiety has been synthesized <1996TL901>. The X-ray analysis showed that the CO bond attached to the triazine ring is only slightly longer (1.23 A) than a standard carbonyl bond. 

Figure 2 The actin-ADP-ribosylating toxins, (a) Molecular mode of action. The actin-ADP-ribosylating toxins covalently transfer an ADP-ribose moiety from NAD+ onto Arg177 of G-actin in the cytosol of targeted cells. Mono-ADP-ribosylated G-actin acts as a capping protein and inhibits the assembly of nonmodified actin into filaments. Thus, actin polymerization is blocked at the fast-growing ends of actin filaments (plus or barbed ends) but not at the slow growing ends (minus or pointed ends). This effect ultimately increases the critical concentration necessary for actin polymerization and tends to depolymerize F-actin. Finally, all actin within an intoxicated cell becomes trapped as ADP-ribosylated G-actin.

Histone ADP-ribosylation was first reported in 1968 [290]. Poly(ADP-ribosylation) has been implicated in several nuclear processes, including DNA replication, repair and recombination [291-294]. Histone HI and the four core histones are modified by adenosine diphospho (ADP) ribosylation which involves the transfer of the ADP-ribose moiety of NAD" " to the histone acceptor (Figs. 1 and 2). HI is the principle poly(ADP-ribosylated) histone, while core histones are ADP-ribosylated to a minor extent [295-297]. HI is modified at Glu residues 2, 14 (or 15), and 116 (or 117) and at Lys located at the C-terminus [25,298,299]. Poly(ADP-ribosylated) HI is associated with dynamically acetylated core histones [295]. There is conflicting results as to whether poly(ADP-ribosylation) of HI promotes chromatin decondensation [300-304]. 

Clawson GA, MacDonald JR, Woo CH. 1987. Early hypomethylation of 2 -0- Ribose moieties in hepatocyte cytoplasmic ribosomal RNA underlies the protein synthetic defect produced by CCK J Cell Biol 105 705-711. 

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