Muscle adenylic acid deaminase

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... 

The enzyme adenylic acid deaminase catalyzes the deamination of AMP to IMP and ammonia. For the HPLC method, the assay involves the separation of the substrate, AMP, from the reaction product IMP. The enzyme is found in muscle. 

An important discovery, that of free adenylic acid in muscle, was made by Embden in 1927. Muscle adenylate was recognized as the 5 -mono-phosphoric ester of adenosine because enzymatic deamination yielded the known inosinic acid. It was shown at that time that the deaminase preparations from muscle did not deaminate the adenylic acid isolated from alkaline hydrolysates of yeast nucleic acid as well, differences were apparent in the chemical properties of the adenylic acids from these two sources. Yeast adenylic acid and the other nucleotides from alkaline hydrolysates of RNA were ultimately shown to be mixtures of the 2 - and 3 -phospho esters. In 1929 the isolation of adenosine triphosphate from muscle was reported by Lohmann and independently by Fiske and Subbarow. The discovery of adenosine diphosphate followed in 1935. 

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. 

Some common examples of enzymes inhibited by phosphate ions include carboxypeptidase, fumarase, urease, phos-phoglucomutase, carboxylase, arylsulphatase and muscle deaminase (for the deamination of adenylic acid). Frequently this inhibition is due to competition of the phosphate with substrates containing phosphate groups or to complex formation with a metal ion essential for the enzyme activity. 

The 5 -adenyhc acid deaminase (22) found in rabbit muscle has been crystallized (23). It converts adenylic acid to inosinic acid and ammonia [Eq. (7)]. The enzyme does not deaminate adenine, adenosine, adenosine diphosphate, adenosine triphosphate, adenosine 2 -phosphate, adenosine S -phosphate, guanosine, or cytosine but does act upon deoxyadenylic acid (24)-... 

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