Adenosine phosphates hydrolysis

These were differently affected by different procedures. For example, when the enzyme was activated at 55°, the increment in ki was slight, but k2 increased 3.5-fold. Similarly, in the presence of EDTA, fc, and k2 values decreased independently, suggesting that the sites for both activities were different. Center and Behai (5) found that with the P. mirabilis enzyme, cyclic 2, 3 -UMP competitively inhibited the hydrolysis of bis(p-nitrophenyl) phosphate. The Ki was 40 pAf very close to the Km for the cyclic nucleotide (Km, 75 yM) which indicated that the two compounds could serve as alternate substrates being hydrolyzed at the same active site. In contrast, 3 -AMP was a mixed inhibitor of cyclic 2, 3 -UMP and bis(p-nitrophenyl) phosphate hydrolysis. Adenosine was a mixed inhibitor of bis(p-nitrophenyl) phosphate hydrolysis but a competitive inhibitor of 3 -AMP hydrolysis. From such kinetic studies Center and Behai (5) suggested that two separate and adjacent sites A and B are involved in the hydrolysis of the diester and phos-phomonoester substrates. Site A serves as a binding site for hydrolysis of ribonucleoside 2, 3 -cyclic phosphates and together with site B catalyzes the hydrolysis of the diester bond. During this reaction 3 -... 

Compounds that serve as energy carriers for the chemotrophs, linking catabolic and biosynthetic phases of metabolism, are adenosine phosphate and reduced pyridine nucleotides (such as nicotinamide dinucleotide or NAD). The structure of adenosine triphosphate (ATP) is shown in Fig. 1. It contains two energy-rich bonds, which upon hydrolysis, yield nearly eight kcal/mole for each bond broken. ATP is thus reduced to the diphosphate (ADP) or the monophosphate (AMP) form. 

The nucleotide anhydride, adenosine 5 -triphosphate (24), when digested with aqueous barium hydroxide, gives a complex mixture containing such products as adenine, adenosine, adenosine 2 -, 3 -, and 5 -phosphates, adenosine 5 -pyrophosphate, and adenosine 2 (or 3 ),5 -diphosphate. - In addition, a nucleotide was foimd in this digest whose structure proved - to be that of adenosine 3 5 -cyclic phosphate (25). This component did not consume metaperiodate, and was degraded enzymically to adenosine 5 -phosphate (26) and adenosine 3 -phosphate (27), without the formation of adenosine 2 -phosphate. Hydrolysis of (25) with an acidic ion-exchange resin did, however, produce the 2 - and 3 -phosphates of adenosine. Compound (25) possessed only one phosphoryl dissociation, and showed a ratio of nucleoside to phosphate of 1 1, which, along with a molecular-... 

Adenylic Acid. Muscle adenylic acid ergaden -ylic acid t -adenylic acid adenosine S -monophosphate adenosine phosphate adenosine-5 -phosphoric add edeno-sine-5. monophosphoric acid A5MP AMP NSC-20264 Addiyl Cardiomone (Na salt) Lycedan My -B-Den My-oston Phosaden. C,0HhNjO7P mol wt 347.23, C 34.59%, H 4.06%, N 20.17%, O 32,25%, P 8,92%. Nucleotide widely distributed in nature. Prepn from tissues Embden, Zimmerman, Z. Physrot Chem. 167, 137 (1927) Embden, Schmidt, ibid. 181, 130 (1929) cf. Kalckar, J. B.ol Chem. 167, 445 (1947). Prepn by hydrolysis of ATP with barium hydroxide Kerr, 3. Biot Chem. 139, 13l (1941). Synthesis Baddiley, Todd. 3. Chem. Soc. 1947, 648. Commercial prepn by enzymatic phosphorylation of adenosine. Monograph on synthesis of nucleotides G. R. Pettit. Synthetic Nucleotides vol, 1 (Van Nostrand-Reinhold. New York, 1972) 252 pp. Crystal structure Kraut, lensen, Acta Cryst 16, 79 (1963). Reviews see Adenosine Nucleic Acids. 

Hulett, H.R., 1970. Non-enzymatic hydrolysis of adenosine phosphates. Nature, 225 1240—1249. 

The use of the phosphoenol pyruvate (PEP)/pyruvate kinase system is probably the most useful method for the regeneration of nucleoside triphosphates [523]. PEP is not only very stable towards spontaneous hydrolysis but it is also a stronger phosphorylating agent than ATP. Furthermore, nucleosides other than adenosine phosphates are also accepted by pyruvate kinase. The drawbacks of this system are the more complex synthesis of PEP [524, 525] and the fact that pyruvate kinase is inhibited by pyruvate at higher concentrations. 

Structure of Coemyme A. The elucidation of the structure of CoA depended heavily on d radation by specific enzymes. The phosphate on carbon 3 of the adenosine was shown to be a monoester phosphate by hydrolysis with prostate phosphomonoesterase. The localization of the monoester at the 3 position was established by its sensitivity to a b nucleotidase that attacks only nucleoside 3 -pbosphates, not 2 - or 5 -phosphates. The original CoA molecule or the phosphatase product, depbospho CoA, can be split by nucleotide pyrophosphatases from potato or snake venom. These reactions permitted the identification of the adenosine phosphate portion of the molecule. The position of the phosphate on pantothenic acid cannot be determined enzymatically, but was established by studies on the synthesis of CoA from synthetic phos-phorylated pantetheines. Pantetheine is split to thiolethanolamine and pantothenic acid by an enzyme found in liver and kidney. This enzyme also attacks larger molecules, including CoA. 

Thiamine can be considered to be the product of the quatemization of 4-methyl-5-(2-hydroxymethyl)thiazole (5) by an active derivative of 4-amino-5-(hydroxymethyl)-2-methyl pyrimidine (4) (Scheme 2). In living cells, pyramine can be activated by conversion into the diphosphate 7, via monophosphate 6, and the substrate of the enzyme responsible for the quatemization is not the thiamine thiazole, but its phosphate 8. The product of the condensation, thiamine phosphate (9), is finally converted into diphosphate 2—the biochemically active derivative—by hydrolysis to free thiamine, followed by diphosphorylation, or more directly, in some cases. Enzymes are known for all of the steps depicted in Scheme 2, and adenosine triphosphate (ATP) is, as usual, the phosphate donor. 

Phosphate also plays a central role in the transmission and control of chemical energy within the cells primarily via the hydrolysis of the terminal phosphate ester bond of the adenosine triphosphate (ATP) molecule (Fig. 14-3b). In addition, phosphate is a necessary constituent of phospholipids, which are important components in cell membranes, and as mentioned before, of apatite, which forms structural body parts such as teeth and bones. It is not surprising, therefore, that the cycling of P is closely linked with biological processes. This connection is, in fact, inseparable as organisms cannot exist without P, and their existence controls, to a large extent, the natural distribution of P. 

Phosphate condensation reactions play an essential role in metabolism. Recall from Section 14.6 that the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) requires an input of free energy ADP -I-H3 PO4 ATP +H2O AG° — +30.6kJ As also described in that section, ATP serves as a major biochemical energy source, releasing energy in the reverse, hydrolysis, reaction. The ease of interchanging O—H and O—P bonds probably accounts for the fact that nature chose a phosphate condensation/hydrolysis reaction for energy storage and transport. 

Attention has been drawn to the potential of phosphoric acid anhydrides of nucleoside 5 -carboxylic acids (14) as specific reagents for investigating the binding sites of enzymes. For example, (14 B = adenosine) inactivates adenylosuccinate lyase from E. coli almost completely, but has little effect on rabbit muscle AMP deaminase. The rate of hydrolysis of (14) is considerably faster than that of acetyl phosphate, suggesting intramolecular assistance by the 3 -hydroxyl group or the 3-nitrogen atom. 

F. H. Westheimer (1987) has provided a detailed survey of the multifarious ways in which phosphorus derivatives function in living systems (Table 4.7). The particular importance of phosphorus becomes clear when we remember that the daily turnover of adenosine triphosphate (ATP) in the metabolic processes of each human being amounts to several kilograms Phosphate residues bond two nucleotides or deoxynucleotides in the form of a diester, thus making possible the formation of RNA and DNA the phosphate always contains an ionic moiety, the negative charge of which stabilizes the diester towards hydrolysis and prevents transfer of these molecules across the lipid membrane. 

The isomerism existing between the pairs of nucleotides was attributed to the different locations of the phosphoryl residues in the carbohydrate part of the parent nucleoside,49 63 since, for instance, the isomeric adenylic acids are both hydrolyzed by acids to adenine, and by alkalis or kidney phosphatase to adenosine. Neither is identical with adenosine 5-phosphate since they are not deaminated by adenylic-acid deaminase,68 60 and are both more labile to acids than is muscle adenylic acid. An alternative explanation of the isomerism was put forward by Doherty.61 He was able, by a process of transglycosidation, to convert adenylic acids a" and 6 to benzyl D-riboside phosphates which were then hydrogenated to optically inactive ribitol phosphates. He concluded from this that both isomers are 3-phosphates and that the isomerism is due to different configurations at the anomeric position. This evidence is, however, open to the same criticism detailed above in connection with the work of Levene and coworkers. Further work has amply justified the original conclusion regarding the nature of the isomerism, since it has been found that, in all four cases, a and 6 isomers give rise to the same nucleoside on enzymic hydrolysis.62 62 63 It was therefore evident that the isomeric nucleotides are 2- and 3-phosphates, since they are demonstrably different from the known 5-phosphates. The decision as to which of the pair is the 2- and which the 3-phosphate proved to be a difficult one. The problem is complicated by the fact that the a and b" nucleotides are readily interconvertible.64,64... 

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