Adenylic acid 5-nucleotidase

The bearing which these discoveries have had on the elucidation of the structure of ribopolynucleotides will be discussed later. It is important to stress here, however, that, for most purposes, the older methods of preparing nucleotides have been superseded by procedures which yield separate isomers of each. Of the techniques mentioned above, paper chromatography iB mainly of analytical value, and is the most convenient method for the qualitative detection of isomeric adenylic acids. The only disadvantage of this method is that the isomers are not completely separable from muscle adenylic acid. The presence of the latter, however, can be readily detected by hydrolyzing it to adenosine by means of the specific 5-nucleotidase present in snake venoms,66 or by deamination by a specific enzyme... 

Nucleoside 2 (or 3 ),5 -diphosphates have been isolated by degradation of certain coenzymes, as well as from hydrolyzates of nucleic acids. Adenosine 3, 5 -diphosphate (see p. 320) has been isolated by enzymic hydrolysis of coenzyme A and from active sulfate (adenosine 3 -phosphate 5 -phosphosulfate). Adenosine 2, 5 -diphosphate was shown to be present in the adenylic acid moiety of the coenzyme adenine-nicotinamide dinucleotide phosphate which, by treatment with a 5 -nucleotidase from potatoes, is converted into adenosine 2 -phosphate. Adenosine 3, 5 -di-phosphate is reported to play a role as a cofactor in the bioluminescence of Renilla reniformis (pansy) Ribonucleic acid carrying a terminal 5 -phos-phate group yields ribonucleoside 3, 5 -diphosphates on digestion with phosphoesterases. ... 

This enzyme has been purified from germinating barley. The purified preparation contains only traces of acid phosphatase, ATPase, and 5-nucleotidase activity. It splits the b or 3 isomers of adenylic acid, inosinic acid, and other nucleotides. 

There are several pathways available for the degradation of the mononucleotides. For example, adenosine 5 -phosphatc (AMP) is either deaminated hydrolytically to inosinic acid (IMP) by 6 -adenylic acid deaminase (217, iS7) or split directly to the corresponding nucleoside, adenosine, by 5 -nucleotidase 238). The nucleoside inosine resulted from either the hydrolysis of inosinic acid by 5 -nucleotidase or by the action of adenosine deaminase on adenosine 238, 239). The above pathways, as well as other likely conversions of purine compounds to hypoxanthine and xanthine 2JiO) are shown in Fig. 13. Finally, the enzyme xanthine oxidase acted on both the free bases, hypoxanthine and xanthine, to produce uric acid which was the final product of purine metabolism in some animals. 

Purine nucleotides are degraded by a pathway in which they lose their phosphate through the action of 5 -nucleotidase (Fig. 22-45). Adenylate yields adenosine, which is deaminated to inosine by adenosine deaminase, and inosine is hydrolyzed to hypoxanthine (its purine base) and D-ribose. Hypoxanthine is oxidized successively to xanthine and then uric acid by xanthine oxidase, a flavoenzyme with an atom of molybdenum and four iron-sulfur centers in its prosthetic group. Molecular oxygen is the electron acceptor in this complex reaction. 

Alkaline phosphatase, acid phosphatase, 5 -nucleotidase, monoacyl hydrolase, ribonuclease, type 1 phosphodiesterase, adenosine triphosphatase, adenyl cyclase, glycosyl transferase, esterases and disaccharidase have been biochemically or cytochemically demonstrated in the tegument of various cestodes (152, 210, 250, 374, 491, 620, 624-626, 651, 718, 763, 776, 898). Several of these enzymes - phosphatases, 5 -nucleotidase and phosphodiesterase - probably have a digestive and/or absorptive function but the role of the others is uncertain. 

---