Adenylyl groups

This enzyme [EC 2.7.T.2], also known as FAD synthase and FAD pyrophosphorylase, catalyzes the ATP-depen-dent transfer of an adenylyl group to FMN to yield FAD and diphosphate. 

Direct hydrolysis of ATP is the source of energy in the conformational changes that produce muscle contraction but, in general, it is not ATP hydrolysis but the transfer of a phosphoryl, pyrophosphoryl, or adenylyl group from ATP to a substrate or enzyme molecule that couples the energy of ATP breakdown to endergonic transformations of substrates. 

Transfer of Phospho, Pyrophospho, and Adenylyl Groups from ATP... 

Adenylyl cyclases. See Adenylate cyclase Adenylyl groups... 

The enzyme complex that catalyses steps d to/of Fig. 25-20 has an unusual composition. An a3 trimer of 23.5-kDa subunits is contained within an icosahe-dral shell of 60 16-kDa (3 subunits, similar to the protein coats of the icosahedral viruses (Chapter 7). The (3 subunits catalyze the formation of dimethylribityllu-mazine (steps d, e), while the a3 trimer catalyzes the dismutation reaction of step/, the final step in riboflavin formation.365 A separate bifunctional bacterial ATP-dependent synthetase phosphorylates riboflavin and adds the adenylyl group to form FAD.366 Two separate mammalian enzymes are required.367 Synthesis of deazaflavins of methanogens (Fig. 15-22) follows pathways similar to those of riboflavin. However, the phenolic ring of the deazaflavin originates from the shikimate pathway.368... 

The transfer of the adenylyl group from ATP to a tyrosine residue is used to regulate some enzymes. The other product of the adenylylation reaction (top) is inorganic pyrophosphate. Hydrolysis of the adenylyl-tyrosine ester bond releases AMP (bottom). 

Phosphopantetheine coenzymes are the biochemically active forms of the vitamin pantothenic acid. In figure 10.11, 4 -phosphopantetheine is shown as covalently linked to an adenylyl group in coenzyme A or it can also be linked to a protein such as a serine hydroxyl group in acyl carrier protein (ACP). It is also found bonded to proteins that catalyze the activation and polymerization of amino acids to polypeptide antibiotics. Coenzyme A was discovered, purified, and structurally characterized by Fritz Lipmann and colleagues in work for which Lipmann was awarded the Nobel Prize in 1953. 

The stereochemistries of tRNA nucleotidyltransferase, which adds the terminal adenylyl group at the -CCA end of tRNA, and DNA-dependent RNA polymerase were elucidated by Eckstein and associates in a two stage study. The E. coli DNA-dependent RNA polymerase study exemplifies their approach. Diastereomer A of ATPaS was copolymerized with UTP using poly(dA-dT)-poly(dA-dT) as the template. The resulting alternating polymer (see Equation 15) was hydrolyzed by ribonuclease A to a cyclic phosphorothioate ... 

The conversion of riboflavin to flavin mononucleotide (FMN) is catalyzed by flavokinase (Figure 9.73). This conversion may occur during absorption through the gut mucosa or in other organs. The subsequent conversion of FMN to flavin adenine dinucleotide (FAD) is catalyzed by FAD synthase. FAD synthase uses ATP as a source of an adenylyl group, in this conversion (McCormick et ah, 1997). Various phosphatases, including those of the gut mucosa, can catalyze the breakdown of FAD to FMN and of FMN to free riboflavin. Dietary flavins that are covalently botmd to proteins are thought to be unavailable and not to contribute to our dietary needs (Bates et ah, 1997). 

I Aminoglycosides s (gentamicin, streptomycin, j amikacin, etc.) Formation of enzymes that inactivate drugs via conjugation reactions that transfer acetyl, phosphoryl, or adenylyl groups... 

Adenylyl cyclase catalyzes an intramolecular adenylyl group transfer of ATP to form 3, 5 -cyclic AMP (cAMP) according to reaction (15). 

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