Adenylate groups

DNA strand. At the expense of one molecule of ATP, two DNA strands are joined via a phosphodi-ester bond. Although eukaryotic and T4 phage DNA ligase use ATP as the adenyl group donor in this reaction, E. coli DNA ligase utilizes NAD+ (Fig. V-16). 

In brief adenylation involves the glutamine-dependent covalent attachment of up to 12 adenyl groups (one per subunit) to a tyrosyl residue of the enzyme subunit, by an adenyltransferase enzyme. The adenylated enzyme has a lower catalytic activity, an absolute requirement for manganese as the divalent cation and is considerably more susceptible to feedback inhibition than the unadenylated enzyme. Deadenylation is catalyzed by the same adenyltransferase as adenylation. Regulation as to which reaction the adenyltransferase catalyzes is modulated by a uridyltransferase which can... 

Adenosine triphosphate Phosphorylation, pyrophosphorylation, transfer- of adenosyl and adenyl groups -... 

Note that the first step in Figure 21.6—reaction of the carboxylate with ATP to give an acyl adenylate—is itself a nucleophilic acyl substitution on phosphorus. The carboxylate first adds to a P=0 bond, giving a five-coordinate phosphorus intermediate that expels diphosphate ion as leaving group. 

In fatty-acid biosynthesis, a carboxylic acid is activated by reaction with ATP to give an acyl adenylate, which undergoes nucleophilic acyi substitution with the — SH group or coenzyme A. (ATP = adenosine triphosphate AMP = adenosine monophosphate.)... 

Acyl CoA s, such as acetyl CoA, are the most common thioesters in nature. Coenzyme A, abbreviated CoA, is a thiol formed by a phosphoric anhydride linkage (0 = P—O—P=0) between phosphopantetheine and adenosine 3, 5 -bisphosphate. (The prefix "bis" means "two" and indicates that adenosine 3, 5 -bisphosphate has two phosphate groups, one on C3 and one on C5. ) Reaction of coenzyme A with an acyl phosphate or acyl adenylate... 

Group II assays consist of those monitoring cellular second messengers. Thus, activation of receptors to cause Gs-protein activation of adenylate cyclase will lead to elevation of cytosolic or extracellularly secreted cyclic AMP. This second messenger phosphorylates numerous cyclic AMP-dependent protein kinases, which go on to phosphorylate metabolic enzymes and transport and regulatory proteins (see Chapter 2). Cyclic AMP can be detected either radiometrically or with fluorescent probe technology. 

Scheme 10.8 Biosynthesis of epothilone. Individual PKS domains are represented as circles and individual NRPS domains as hexagons. Acyl carrier proteins (ACPs) and thiola-tion domains (T) are posttranslationally modified by a phos-phopantetheinyl group to which the biosynthetic intermediates are covalently bound throughout the chain assembly. The thioesterase domain (TE) cyclizes the fully assembled carbon chain to give the 16-membered lactone. Following dehydration of Cl 2—Cl 3 to give epothilones C and D, the final step in epothilone biosynthesis is the epoxidation of the C12=C13 double bond by the cytochrome P450 enzyme P450epol<. KS ketosyn-thase KS(Y) active-site tyrosine mutant of KS AT acyltransfer-ase C condensation domain A adenylation domain ...

The following schemes represent the overall reaction of firefly bioluminescence (McElroy and DeLuca, 1978), where E is luciferase LH2 is D-luciferin PP is pyrophosphate AMP is adenosine phosphate LH2-AMP is D-luciferyl adenylate (an anhydride formed between the carboxyl group of luciferin and the phosphate group of AMP) and L is oxyluciferin. 

Fig. 6.3.5 A reaction scheme proposed by Tsuji (2002) for the Watasenia bioluminescence. The proposed mechanism involves the adenylation of luciferase-bound luciferin by ATP, like in the bioluminescence of fireflies. However, the AMP group is split off from luciferin before the oxygenation of luciferin, differing from the mechanism of the firefly bioluminescence. Thus the role of ATP in the Watasenia bioluminescence reaction remains unclear. Reproduced with permission from Elsevier.

The OP group of receptois share common effector mechanisms. All receptois couple via pertussis toxin-sensitive Go and Gi proteins leading to (i) inhibition of adenylate cyclase (ii) reduction of Ca2+ currents via diverse Ca2+ channels (hi) activation of inward rectifying K+ channels. In addition, the majority of these receptors cause the activation of phospholipase A2 (PLA2), phospholipase C 3 (PLC 3), phospholipase D2 and of MAP (mitogen-activated protein) kinase (Table 3). 

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