3’, 5’-Cyclic adenylic acid

Nucleosides and nucleotides are found in places other than as part of the structure of DNA and RNA. We have seen, for example, that adenosine units are part of the structures of two important coenzymes, NADH and coenzyme A. The 5 -triphosphate of adenosine is, of course, the important energy source, ATP (Section 22. IB). The compound called 3, 5 -cyclic adenylic acid (or cyclic AMP) (Fig. 25.6) is an important regulator of hormone activity. Cells synthesize this compound from ATP through the action of an enzyme, adenylate cyclase. In the laboratory, 3, 5 -cyclic adenylic acid can be prepared through dehydration of 5 -adenylic acid with dicyclohexylcarbodiimide. 

FIGURE 25.6 3, 5 -Cyclic adenylic acid (cyclic AMP) and its biosynthesis and laboratory synthesis. 

When 3, 5 -cyclic adenylic acid is treated with aqueous sodium hydroxide, the major product that is obtained is 3 -adenylic acid (adenosine 3 -phosphate) rather than 5 -adenyhc acid. Suggest a mechanism that explains the course of this reaction. 

In muscle phosphorylase, the passage from the inactive to the active form is stimulated only by epinephrine. (It has been suggested that in the liver fluke. Fasciola hepatica, serotonin stimulates phosphorylase. In this fluke, serotonin also stimulates phosphofruc-tokinase, probably through the intermediate of 3, 5 -cyclic adenylic acid.) In liver, both epinephrine and glucagon stimulate the activity of the phosphorylase. In liver, the activation has been demonstrated in vivo in cell-free preparations epinephrine does not act directly on phosphorylase, but it stimulates the formation of 3, 5 -cyclic adenylic acid, which in turn catalyzes the conversion of inactive phosphorylase to active phosphorylase in the supernatant. The cyclic nucleotide is formed from ATP in the presence of a particulate enzyme (adenine cyclase), which is found in heart, muscle, liver, brain, and other organs. The reaction requires magnesium, and, as can be expected, 3, 5 -cyclic adenosine accumulates when the medium contains fluoride. 

Another cyclization of 3 -adenylic acid (3 -AMP) to 2, 3 -cyclic adenylic acid (2, 3 -cAMP) took place by condensation with carbiminodiimidazole (or iV-cyanoimidazole) in aqueous or anhydrous medium. It is supposed that the reaction of 3 -AMP probably proceeds via a phosphoric imidazolide [9]... 

Adenosine-3 -monophosphoric acid hydrate [3 -adenylic acid, 3 -AMP] [84-21-9] M 347.3, m 197°(dec, as 2H2O), 210°(dec), m 210°(dec), [a]s46 -50° (c 0.5, 0.5M Na2HP04), pK 3.65, pKz 6.05. It crystallises from large volumes of H2O in needles as the monohydrate, but is not very soluble in boiling H2O. Under acidic conditions it forms an equilibrium mixture of 2 and 3 adenylic acids via the 2, 3 -cyclic phosphate. When heated with 20% HCl it gives a quantitative yield of furfural after 3hours, unlike 5 -adenylic acid which only gives traces of furfural. The yellow monoacridine salt has m 175°(dec) and... 

Ribonuclease T2 is regarded as a nonspecific endoribonuclease [EC 2.7.7.17, ribonucleate nucleotido-2 -transferase (cyclizing)]. It preferentially splits the internucleotide bonds between the 3 -adenylic acid group and the 5 -hydroxyl group of adjacent nucleotides in RNA, with the intermediary formation of adenosine 2, 3 -cyclic phosphate and splits consequently all secondary phosphate ester bonds of other nucleotides in RNA via the nucleotides 2, 3 -cyclic phopshates. 

Adenosine 2, 3 -cyclic phosphate is scarcely accumulated, though other nucleoside 2, 3 -cyclic phosphates are accumulated as intermediates. This result suggests that the action of RNase T2 on RNA is owing to the cooperation of an adenylic acid specific endonuclease activity and a nonspecific exonuclease activity releasing mononucleotides from the 3 terminal. 

Ribonuclease Ua digestion of ApU has revealed reduced hydrolase activity in the second step of RNase U2 action (30). When 87.4% of ApU was readily degraded to produce uridine and adenosine 2, 3 -cyclic phosphate, no 3 -adenylic acid was detected. After exhaustive degradation of ApU, hydrolysis of adenosine 2, 3 -cyclic phosphate occurred and 3 -adenylic acid gradually appeared. 

CAS 61-19-8. C10H14N5O7P. The monophosphoric ester of adenosine, i.e., the nucleotide containing adenine, d-ribose, and phosphoric acid. Adenylic acid is a constituent of many important coenzymes. Cyclic adenosine-3, 5 -monophosphate is designated by biochemists as cAMP. 

The degradation of cyclic AMP is catalyzed by a specific phosphodiesterase which converts it to adenylic acid " (Figure l). Again, the effect of nucleotide analogues or other potential inhibitors on the degradation of cyclic AMP can be studied vitro in this enzyme system, and the possible significance of such agents will be discussed below. 

Adenylic acids o and b were each converted by trifluoroacetic anhydride into the same 2 3 -cyclic phosphate (13, R = adenin-9-yl) by Brown, Magrath, and Todd. These authors also applied this method to the synthesis of 2 3 -cyclic phosphates (13) of cytidine, uridine, and guanosine. Hydrolysis of these cyclic phosphates gave the corresponding a and b nucleotide mixtures. Markham and Smith found that, during hydrolysis of ribonucleic acid with pancreatic ribonuclease, the 2 3 -cyclic phosphates of the pyrimidine nucleosides are formed as intermediates leading to the ribonucleoside phosphates b. The also showed that 2 3 -cyclic phosphates (13) are formed by very mild, alkaline hydrolysis of ribonucleic acid. The discoveries of these a and b isomers of mononucleotides from... 

Abbreviations used NAD+ = nicotinamide adenine dinucleotide NADH e reduced nicotinamide adenine dinucleotide NADP = nicotinamide adenine dinudeotide phosphate NAD PH reduced nicotinamide adenine dinucleotide phosphate NMN, NMN+ nicotinamide mononucleotide NMNH2 = reduced nicotinamide mononucleotide a-NAD a-nicotinamide adenine dinucleotide AMP = 5 -adenylic acid 3,5 -AMP adenosine 3, 5 -cycIic phosphate 3 ,5 -UMP = uridine 3, 5 -cyclic phosphate 3, 5 -CMP cytidine 3, 5-cyclic phosphate 3 f5 GMP = guanosine 3 5f-cyclic phosphate 3, 5 TMP thymidine 3, 5 -cyclic phosphate Dibutyryl-3, 5 -AMP = N6,02-dibutyryladenosine 3, 5 -cyclic phosphate 2, 3 -UMP = uridine 2 ,3 -cyclic monophosphate 2, 3 -CMP cytidine 2, 3 -cyclic monophosphate 2, 3 -AMP = adenosine 2, 3 -cyclic monophosphate 2 ,3 -GMP = guanosine 2 3 -cyclic monophosphate 2 -UMP = uridine 2 -phosphate -UMP uridine -phosphate 5 -UMP = uridine 5 phosphate Poly U polyuridylic acid ADP = adenosine 5 -diphosphate FAD = flavin adenine dinucleotide UpA, UpU, ApU and ApA x dinucleoside phosphates of uridine and/or adenine. c See original references for experimental conditions and additional data. 

The different varieties of orthophosphoric monoesters and diesters which are present in all living species are exceedingly numerous. Biologically important monoesters include the mononucleotides such as, for example, adenylic acid (adenosine monophosphate, AMP), inosinic acid, vitamin Bg and many phosphorylated proteins, for example, milk caseins. Biologically important diesters include the phospholipids (e.g. lecithin and phosphatidyl inositol), plasmalogens, sphingomyelins, cyclic nucleotide monophosphates (e.g. cyclic AMP), some teichoic acids, vitamin Bj2 and of course the immensely important nucleic acids (polynucleotides) (Chapters 10 and 11). The great stability of diesters is an essential feature of the chemistry of polynucleotides. 

Mammalian tissues do not contain adenine deaminase, but specific enzymes able to deaminate adenosine and 5 -adenylic acid have been found in a variety of mammals. Adenosine deaminase activity has been detected in intestine, liver, spleen, brain, kidney, heart, and skeletal muscle. Adenosine deaminase has been partially purified from the intestinal mucosa. The enzyme has a great affinity for adenosine and deoxyadenosine and only low affinity for 2 -AMP and 3, 3 -cyclic AMP. Its activity is lost on dialysis. The enzyme acts optimally at pH 7. 

Another hypothesis describing the mode of action of ACTH has recently gained some support. It proposes that ACTH modifies cellular permeability through the intermediate of adenosine-3, 5 -mono-phosphate. The increased penetration of xylose and a-aminoisobutyric acid under the influence of ACTH has been established. It also has been proposed that ACTH stimulates the formation of cyclic adenylate, which in turn induces the synthesis of new mitochondrial proteins. The appearance of the new protein is associated with the development of activity of the enzyme involved in the conversion of cholesterol to pregnenolone. 

Under the influence of ACTH, free fatty acids and glycerol concentrations increase in adipose tissue. ACTH stimulates lipolysis in adipose tissue by activating a hormone-sensitive lipase. However, ACTH does not act directly on the lipase. There are at least two other intermediate messengers adenylate cyclase and cyclic adenylate. The molecular mechanism of action of ACTH on lipolysis will be discussed in more detail in the section devoted to adipose tissue metabolism. 

Several other phosphodiesterases have been described, such as ri-bonuclease Ti from takadiastase. This enzyme hydrolyzes RNA and the RNA core produced by pancreatic ribonuclease, with the rapid liberation of guanosine 3 -phosphate and guanosine 2, 3 -cyclic phosphate. A second enzyme from the same source, ribonuclease Tj, rapidly liberates adenylic acid and pyrimidine mononucleotides while guanosine 3 -phosphate is liberated slowly (161). 

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