Ribosylation, adenine

Adenine, 9- -D-2-deoxyribofuranosyl-, 5, 536 Adenine, 8-(2-deoxy-/3-D-ribosyl)-synthesis, 5, 585 Adenine, 2,8-dialkyl-synthesis, 5, 569 Adenine, 2,8-dichloro-reactions... 

G proteins can be modified by ADP-ribosylation catalyzed by certain bacterial toxins. Among the tools that facilitated the discovery and characterization of G proteins were the bacterial toxins cholera and pertussis, which were known to influence adenylyl cyclase activity. Subsequently, it was shown that the actions of these toxins are achieved by their ability to catalyze the addition of an ADP-ribose group donated from nicotinamide adenine dinucleotide (NAD) to specific amino acid residues in certain heterotrimeric G protein a subunits [ 1 ]. 

BRCT BRCAl C-terminus-like DBD DNA-binding domain dPARP Drosophila PARP MPTP l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine NAD+ Nicotinamide adenine dinucleotide NAm Nicotinamide NLS Nuclear locahzation signal OAADPR O-acetyl-ADP-ribose PAR Poly(ADP-ribose) PARG Poly(ADP-ribose) glycohydrolase PARP Poly(ADP-ribose) polymerase PARylation poly(ADP-ribosyl)ation... 

The sirtuins (silent information regulator 2-related proteins class III HDACs) form a specific class of histone deacetylases. First, they do not share any sequence or structural homology with the other HDACs. Second, they do not require zinc for activity, but rather use the oxidized form of nicotinamide adenine dinucleotide (NAD ) as cofactor. The reaction catalyzed by these enzymes is the conversion of histones acetylated at specific lysine residues into deacetylated histones, the other products of the reaction being nicotinamide and the metabolite 2 -0-acetyl-adenosine diphosphate ribose (OAADPR) [51, 52]. As HATs and other HDACs, sirtuins not only use acetylated histones as substrates but can also deacetylate other proteins. Intriguingly, some sirtuins do not display any deacetylase activity but act as ADP-ribosyl transferases. 

This enzyme [EC 2.4.2.21] catalyzes the reaction of /3-nicotinate D-ribonucleotide with dimethylbenzimidazole to produce nicotinate and Af -(5-phospho-a-D-ribosyl)-5,6-dimethylbenzimidazole. Benzimidazole also serves as a substrate. The clostridial enzyme acts on adenine to produce 7-a-D-ribosyladenine 5 -phosphate. 

Finally, the adenine and ribosyl groups of ATP, ADP, and AMP provide additional structural features that allow these molecules to bind to enzymes and thus to participate in regulating enzymatic activities. This may be part of the reason that no known organisms base their energy-transfer reactions entirely on inorganic pyrophosphate or other polyphosphate compounds without a nucleoside moiety. 

The mechanism of the /V6-acyladeninc and silylating method for the ribosylation of adenine has been determined.131 The kinetic product formed by ribosylation at N(l) has been isolated. The reaction occurs here because the N(7) position is sterically... 

Aromatic cytokinins are found in poplar,379-381 anise,382 tomato,383 Cocos nucifera m and Arabidopsis,381 In addition to BA, aromatic cytokinins are found as ortho-topolins, wc/ -topolins, hydroxylated BAs, ortho-meth-oxytopolins, and rwfto-methoxytopolins (Figure 1 1).380,381 Other derivatives have been isolated as N3-, N7-, and /VP-glucosides and A P-alanine on the adenine ring,385 and nucleosides and a glucoside linked to the ribosyl moiety.386 In spite of the several reports of their occurrence, it is not clear whether the aromatic species are common in plants. 

The second messengers cADPR (in which both N1 and N8 of adenine are ribosylated) and NAADP (in which the nicotinamide of oxidized nicotinamide adenine dinucleotide... 

It has been shown that the accumulation of 5-amino-iV-D-ribosyl-4-imidazolecarboxamide in a purine-requiring mutant of Escherichia coli ceases when the bacteria are supplied with an excess of purine. The site of inhibition is, apparently, before the formation of the imidazole ring occurs, but after the formation of the D-ribosyl moiety, since adenine has only a... 

The nicotinamide nucleotide coenzymes function as electron carriers in a wide variety of redox reactions. In addition, NAD is the precursor of adenine dinucleotide phosphate (ADP)-ribose for ADP-ribosylation and poly(ADP-ribosylation) of proteins and cADP-ribose and nicotinic acid adenine dinucleotide phosphate (NAADP). They act as second messengers and stimulate increases in intracellular calcium concentrations. 

NAD is the source of ADP-ribose for the modification of proteins by mono-ADP-ribosylation, catalyzed by ADP-ribosyltransferases (Section 8.4.2), and poly(ADP-ribosylation), catalyzed by poly(ADP-ribose) polymerase (Section 8.4.3). It is also the precursor of two second messengers that act to increase the intracellular concentration of calcium, cADP-ribose, and nicotinic acid adenine dinucleotide phosphate (Section 8.4.4). 

Poly(ADP-ribose) polymerase (PADPRP) hypothesis. - In this theory DNA is the initial target of the mustard agent. Alkylated DNA purines undergo spontaneous and enzymatic depurination, leading to the production of apurinic sites which are cleaved by apurinic endonucleases to yield DNA breaks. Accumulation of DNA breaks leads to activation of the chromosomal enzyme PADPRP, which utilizes nicotinamide adenine dinucleotide (NAD ) as a substrate to ADP-ribosylate and a variety of nuclear... 

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