AMP catabolism

THE PATHWAY OF AMP CATABOLISM AND ITS CONTROL IN ISOLATED RAT HEPATOCYTES SUBJECTED TO ANOXIA... 

In the second experiment, the rapid degradation of AMP by pigeon liver was mediated almost entirely by phosphatase action rather than by deamination (67). Since the specific activity of IMP formed from small precursors in incubated homogenates was unaffected by the simultaneous breakdown of adenylic acid, it was concluded that adenosine, rather than IMP, was the first product of AMP catabolism. If IMP were formed from AMP the specific activity of IMP would have been lowered. 

The answer in practice is ATP though you would have been theoretically correct if you had said ADP and AMP. Indirectly, NAD+ or NADH are also compounds which regulate the anabolic/catabolic balance. 

Ampe F, D Leonard, ND Bindley (1998) Repression of phenol catabolism by organic acids in Ralstonia eutro-pha. Appl Environ Microbiol 64 1-6. 

This reaction is fully reversible, so after the intense demand for ATP ends, the enzyme can recycle AMP by converting it to ADP, which can then be phosphorylated to ATP in mitochondria A similar enzyme, guanylate kinase, converts GMP to GDP at the expense of ATP. By pathways such as these, energy conserved in the catabolic production of ATP is used to supply the cell with all required NTPs and dNTPs. 

ATP is the chemical link between catabolism and anabolism. It is the energy currency of the living cell. The exergonic conversion of ATP to ADP and Pi, or to AMP and PPi, is coupled to many endergonic reactions and processes. 

Feedback can also be positive. Since AMP is a product of the hydrolysis of ATP, its accumulation is a signal to activate key enzymes in metabolic pathways that generate ATP. For example, AMP causes allosteric activation of glycogen phosphorylase, which catalyzes the first step in the catabolism of glycogen. As is shown in Fig. 11-5, the allosteric site for AMP or IMP binding is more than 3 nm away from the active site. Only a... 

Purine bases from ingested foods, or formed by catabolism of nucleic acids, are able to react with PRPP under the influence of phosphoribosyltransferases.3063 Two such enzymes are known to act on purines. One converts adenine to AMP (Fig. 25-17, step b) and also acts upon 5-aminoimidazole-4-carboxamide. This enzyme may be especially important to parasitic protozoa such as Leishmania, which lack the de novo pathway of purine synthesis (Fig. 25-15).278/306b... 

A highly purified FDPase from the slime mold Polysphondylium pallidum has been shown (92), to hydrolyze both FDP and SDP, at nearly equal rates, to yield fructose 6-phosphate and sedoheptulose 7-phosphate, respectively. In other respects the purified enzyme was remarkably similar to that isolated from Candida utilis it was completely inactive at pH 7.5 or 8.0, and showed a pH optimum at 9.2. In the presence of low concentrations of EDTA a second pH optimum appeared at pH 7.5. Unlike the Candida FDPase, however, the Polysphondylium enzyme was not inhibited by AMP at any pH. The levels of enzyme which could be extracted from the cells did not change significantly during the various stages of differentiation, and its activity could not be related to catabolic or anabolic processes which characterize these stages. 

Adenine phosphoribosyltransferase catalyzes the conversion of adenine to AMP in many tissues, by a reaction similar to that of hypoxanthine-guanine phosphoribosyltransferase, but is quite distinct from the latter. It plays a minor role in purine salvage since adenine is not a significant product of purine nucleotide catabolism (see below). The function of this enzyme seems to be to scavenge small amounts of adenine that are produced during intestinal digestion of nucleic acids or in the metabolism of 5 -deoxy-5 -methylthioadenosine, a product of polyamine synthesis. 

Most of the free purines derived from the breakdown of DNA, RNA, and nucleotides in the diet are catabolized to xanthine and then to uric acid in the gut mucosa. The AMP and GMP biosynthesized in the body can also be bmken down to free purines, such as adenine, guanine, and hypoxanthine. These purines, in contrast to those derived frcim the diet, are largely reused for the synthesis of ATP and GTP- They are first converted back to AMP or GMP in a pathway of reutiliza-lion called the purine salvage pathway. For example, adenine phosphoribosyl-transferase (PRPP) catalyzes the conversion of adenine to AMP. Here, PRPP serves as the source of the phosphoribose group. Pyrophosphate is a product of the reaction. 

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