Adenosine monophosphate biosynthesis

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.)... 

Traub O, Look J, Paul D, Willecke K Cyclic adenosine monophosphate stimulates biosynthesis and phosphorylation of the 26 kDa gap junction protein in cultured mouse hepatocytes. Eur J Cell Biol 1987 43 48-54. 

The ATP molecule contains pyrophosphate linkages (bonds formed when two phosphate units are combined together) that release energy when needed. ATP can be hydrolyzed in two ways the removal of terminal phosphate to form adenosine diphosphate (ADP) and inorganic phosphate, or the removal of a terminal diphosphate to yield adenosine monophosphate (AMP) and pyrophosphate. The latter is usually cleaved further to yield two phosphates. This results in biosynthesis reactions, which do not occur alone, that can be driven in the direction of synthesis when the phosphate bonds are hydrolyzed. 

The actual biosynthesis of purines (illustrated below in abbreviated form for the nucleotide adenosine monophosphate AMP 10.9) involves construction of a pyrimidine ring onto a pre-formed imidazole. 

Still about saponin 1,87, isolated from A. membranaceus, Zhang et al. [317] report that this substance induces the accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanidine monophosphate (cGMP) in rabbit plasma and affects DNA biosynthesis in partially... 

The effect of light in combination with exogenous precursors on amaranthin biosynthesis has been studied, as has the effect of cyclic 3, 5 -adenosine monophosphate. ... 

It is widely known that cyclic nucleotides are involved in fundamental processes, which include those related to platelet aggregation. In this way, the inhibition of the enzyme phosphodiesterase could be one such mechanism through its effect on cAMP (Cyclic Adenosin Monophosphate) and cGMP (Cyclic Guanosine Monophosphate) [117], Another mechanism might involve inhibition of cycloxygenase, with a consequent depression of thromboxane A2 biosynthesis [115] as well as some influence on the inhibition of the intracellular mobilization of Ca2+ flux and its influx across the plasma membrane, as happens with genistein [118]. 

Luteinizing hormone binds to its receptor on the surface of the Leydig cells to initiate testosterone biosynthesis. As in other endocrine cells, the binding of gonadotropin activates the Gs signal transduction pathway, increasing intracellular cyclic adenosine monophosphate (cAMP) levels via activation of adenylate cyclase. One of the processes influenced by elevated cAMP levels is the... 

Biosynthesis of TRH occurs in a wide area of the hypothalamus and appears to be under the control of a nonribosomal (soluble) enzyme system, TRH synthetase (R5), which is activated by norepinephrine (G15). TRH is stored in the median eminence, from which is secreted into the hypophysial venous portal system to be transported to the anterior pituitary gland (R2). There it is specifically bound to membrane receptors (G13, W3) and activates adenyl cyclase, leading to increased production of cyclic adenosine monophosphate (K1). 

The initial step in cytokinin (adenine derivatives with an isoprenoid side chain) biosynthesis is Al-prenylation of adenosine 5-phosphate, a reaction catalyzed by adenosine phosphate-isopentenyltransferases (PTs). PTs catalyze the isopropene unit transfer reaction to an acceptor (adenosine monophosphate, AMP) which serves as a nucleophile. The latter is alkylated by DMAPP to form, by an Sivf2-nucleophilic displacement reaction, a prenylated AMP and pyrophosphate (PP) as products [14, 15]. 

In the second stage, the m-RNA serves as the template for the formation of polypeptide chains at the biosynthesis site (in the ribosomes). The a-aminocarboxylic acids necessary for this are joined by means of their carboxyl groups to transfer RNA (r-RNA), which has a molecular weight of 25,000. The energy necessary for the addition of the a-aminocarboxylic acids is provided by the conversion of adenosine triphosphate to adenosine monophosphate (ATPAMP). A specific enzyme is necessary for the addition of each aminocarboxylic acid to the growing peptide chain, i.e., at least 20 different enzymes are necessary ... 

The dinucleotide NAD" (and NADH, NAD(P)", and NAD(P)H) is composed of ADP and a second ribosyl unit to which a nicotinamide is appended at the anomeric carbon. The biosynthesis of adenosine monophosphate (adenosine 5 -phosphate, AMP) was outlined above, and AMP can be converted to ADP by the action of adenylate kinase (EC 2.7.4.3). The enzymes called ATP synthases (EC 3.6.3.14 and 3.6.3.15) are complicated membrane- and nonmembrane-associated species that convert the energy associated with proton electrochemical gradients into ATP from ADP and inorganic phosphate (Pi) (Chapter 14). 

Nucleotide biosynthesis, like nucleotide catabolism, is relatively complex. Thus, we ll again look at only one example, adenosine monophosphate. Purine nucleotides are formed by initial attachment of an -NH2 group to ribose, followed by multistep buildup of the heterocyclic base. The attachment of -NH2 takes place by a nucleophilic suhstitution reaction of ammonia with 5-phosphoribosyl a-diphosphate to give /3-5-phosphorihosylamine and probably involves an SNl-like loss of diphosphate ion with formation of an 0x0-nium-ion intermediate. Although we ll not cover the details of its formation, inosine monophosphate (IMP) is the first fully formed purine ribonucleotide, with adenosine monophosphate (AMP) derived fi-om it. 

Show the mechanism of the formation of adenosine monophosphate from adenylosuccinate, the third step in adenosine biosynthesis (Figure 24.12). 

The Hofmann elimination reaction is not often used today in the laboratory, but analogous biological eliminations occur frequently, although usually with protonated ammonium ions rather than quaternary ammonium salts. In the biosynthesis of nucleic acids, for instance, a substance called adenylosuccinate undergoes an elimination of a positively charged nitrogen to give fumarate plus adenosine monophosphate. 

The input of energy in the form of the hydrolysis of ATP to either ADP and Pi or to adenosine monophosphate (AMP) and pyrophosphate powers the synthesis of biological molecules, including, as we have seen, carbohydrates in photosynthesis, proteins, DNA, RNA, and fatty acids. To delve into the role of ATP in biosynthesis in depth is not possible in this brief article. Aspects of fatty acid biosynthesis, however, reveal interesting principles of the energetics of biosynthetic pathways. 

The phosphate group can also form cyclic esters and this is observed in the case of the biosynthesis of cyclic adenosine monophosphate (cAMP) (Fig. 5.53), which is an important intracellular messenger formed within cells, for... 

---