5’-nucleotidase activity

CarbocycHc 2/3 -didehydro-2/3 -dideoxyguanosine [118353-05-2] (carbovk, CBV, 66), C H 2N502, synthesized in 1988 (177), is a promising candidate for the chemotherapy of AIDS. CBV inhibits HIV repHcation and HIV-induced cytopathic effects in a variety of human T-lymphoblastoid ceU lines at concentrations approximately two hundred- to four hundredfold below its cytotoxic concentrations (177). CBV is as effective as AZT and DDC in reducing the expression of vkal antigen in HIV-infected CEM ceUs (177). The antivkal potency and selectivity of carbovk is comparable to the anti-HIV-1 potency and selectivity of 2/3 -dideoxyadenosine (178). The exact mode of antivkal action of carbovk has not yet been elucidated, but may be the modulating effect of intraceUular nucleotides on 5 -nucleotidase activity (179). 

Alanko, L., Heiskanen, S., Stenberg, D. Porkka-Heiskanen, T. (2003a). Adenosine kinase and 5 -nucleotidase activity after prolonged wakefulness in the cortex and the basal forebrain of rat. Neurochem. Int. 42 (6), 449-54. 

Certain enzymes shown to be present in myelin could be involved in ion transport. Carbonic anhydrase has generally been considered a soluble enzyme and a glial marker but myelin accounts for a large part of the membrane-bound form in brain. This enzyme may play a role in removal of carbonic acid from metabolically active axons. The enzymes 5 -nucleotidase and Na+, K+-ATPase have long been considered specific markers for plasma membranes and are found in myelin at low levels. The 5 -nucleotidase activity may be related to a transport mechanism for adenosine, and Na+, K+-ATPase could well be involved in transport of monovalent cations. The presence of these enzymes suggests that myelin may have an active role in ion transport in and out of the axon. In connection with this hypothesis, it is of interest that the PLP gene family may have evolved from a pore-forming polypeptide [9],... 

Thus, there is likely as many as three enzymes with 5 -nucleotidase activity in liver, one lysosomal, one cytoplasmic, and one membrane bound. Their specificities and kinetic properties appear to be distinctly different. This would suggest specialized physiological functions not yet understood. 

The enzyme in the myocardium has recently attracted attention because of the possibility that adenosine is a physiological regulator of coronary blood flow (67) (adenosine is a potent coronary dilator). Most of the 5 -nucleotidase activity in rat heart is membrane bound, and a partially purified preparation has been obtained by extracting acetone powder preparations with deoxycholate (68). All 5 -nucleotides are hydrolyzed. The enzyme is strongly inhibited competitively by ATP (Ki 1.8 fxM). Whether this provides a regulatory mechanism for adenosine formation in the heart is not known. 

The presence of an enzyme with 5 -nucleotidase activity in extracts of potato were referred to by Heppel (1). The enzyme has been purified 200-fold by Klein (82) and studied kinetically (83). All major 5 -nucleotides are hydrolyzed at similar rates. The preparation also hydrolyzed 3 -nucleotides at a substantial rate (20-30% that of 5 -AMP). However, kinetic data (83) suggested that the purified preparation was perhaps a mixture of specific 5 - and 3 -nucleotidases. 

The accumulation of adenosine in hypoxic tissues can also be explained by the hypoxia-mediated upregulation of 5 -nucleotidase activity, an enzyme that converts AMP to adenosine, which results in the accumulation of extracellular adenosine... 

We discuss two assays for the measurement of pyrimidine 5 -nucleotidase activity. In the first, as described by Sakai et al. (1982), a pyrimidine nucleoside 5 -phosphate is hydrolyzed to form the corresponding pyrimidine nucleoside. 

Figure 10.11 AMP can be formed by adenosine kinase (1) in a reaction that uses ATP as the phosphate donor and forms ADP as the second reaction product. Alternatively, AMP can be deaminated to IMP by the enzyme AMP deaminase (2) and converted to inosine (INO) by a 5 -nucleotidase activity (3). Finally, AMP can be phosphorylated to ADP by the enzyme AMP kinase (4).

Arnmerman, J. W., and Azam, F. (1985). Bacterial 5 -nucleotidase activity in aquatic ecosystems A novel mechanism of phosphorus regeneration. Science 227, 1338-1340. 

Fukano, M., Amano, S., Hazama, F., Hosoda, S. 5 -nucleotidase activities in sera and liver tissues of viral hepatitis patients. Gastroenterol. Japon. 1990 25 199-205... 

Fig. 59. 5 -Nucleotidase immunohistochemical staining of rat cerebellum. A. Immunofluorescence. B. PAP-method. Enzyme activity is predominantly found within the molecular layer on Bergmann glial fibers (long arrows). Purkinje cells are surrounded by fine rims of reaction product (small arrows). Within the granular layer 5 -nucleotidase activity is diffusely scattered between granule cells (arrow heads). Vibratome sections. C. Longitudinally sectioned Bergmann glia cell processes (B) of the molecular layer of rat cerebellum. Fine DAB reaction product is located on adjacent membranes of these processes (arrows). Bars in A,B = 50 /tm, in C = 0.5 nm. Schoen et al. (1987).

Marani E (1977) The subcellular distribution of 5 -nucleotidase activity in mouse cerebellum. Exp. Neurol, 57, 1042-1048. 

Carakostas, M. C., R. J. Power, and A. K. Banerjee.1990. Serum 5 -nucleotidase activity in rats A method for automated analysis and criteria for interpretation. Veterinary Clinical Pathology 19 109-113. 

Dooley, J. R, and L. Racich. 1980. A new kinetic determination of serum 5 -nucleotidase activity with modifications for a centrifugal analyzer. Clinical Chemistry 26 1291-1297. 

Bacterial 5 -nucleotidase activity was first noted in marine systems as a means of turning over 5 -mononucleotides, conceivably released by phosphodiesterase or exonucleolytic activity (Ammerman and Azam, 1985). Although alkaline phosphatase can hydrolyse these substrates, it can be distinguished from 5 -nucleotidase activity by its sensitivity to micromolar concentrations of phosphate 5 -nucleotidase was virtually unaffected by 100 p,M phosphate, while 80% of alkaline phosphatase activity was lost under the same conditions (Ammerman and Azam, 1991a). Further, 5 -nucleotidase was competitively inhibited by 5 -guanidyl monophosphate, but almost completely... 

Upon purification, the K -stimulated phosphatase activity is always copurified with the (K )-ATPase activity [63-65]. Mitochondrial markers, such as cytochrome c oxidase, succinate dehydrogenase, monoamino-oxidase, and the ribo-somal marker RNA are largely removed by the purification procedure. The same is true for the anion-sensitive ATPase and 5 nucleotidase activities, but some (Na — K )-ATPase activity is still present in highly purified (K" -I-H )-ATPase preparations. Purification is also characterised by a lowering of the K -insensitive Mg ATPase activity, but even in the purest preparations some Mg -ATPase activity (4% of (K -I- H )-ATPase activity) is still present. This may represent an impurity or an inherent property of the enzyme. 

M. Smith, A, J, Patel, A, E, Kingsbury, A, Hunt, and R. Balazs, Effects of thyroid state on brain development -adrenergic receptors and 5 -nucleotidase activity. Brain Res. 198 375-387 (1980). 

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