In central nervous system, ecto-purine and ecto-pyrimidine nucleotides play a role in neurotransmission and neuromodulation of neurons and glia cells. The source of ecto-purines in the CNS is exocitosis from all type of brain cells, endothelial and blood cells. Ecto-purines cooperate with two classes receptors: P1-adenosine receptors and P2-nucleotide receptors.

Concentration of ecto-nucleotides and ecto-nucleosides is regulated by soluble exo-enzymes and ecto-enzymes bound to cell membrane. These enzymes are involved in termination of nucleotide signal and may produce other messengers (ADP and adenosine). Previous research showed presence nucleotides and nucleosides in cerobrospinal fluid (CSF) and nucleotide P2X₂ receptor on the surfaces of the cerebrospinal fluid contacting neurons. Also, the activity of ENTPDases was found in the rat CSF, and activity of ecto-adenosine deaminase in human CSF. Additionally, our unpublished results show, that there are number of nuclotidases bound to cell membrane of ependyma.

The aim of this research was to identify the enzymes metabolizing purines and pyrimidines in the cerebrospinal fluid.

Using the immunodetection and catalytic study of CSF of patients with neurological diseases we detected an activity of soluble adenylate kinase and enzymes which belong to NTPDases and NPPases. Both these hydrolases require an alkaline pH, while the optimal pH for adenylate kinase is 6.5. NPPases of CSF prefer ATP as a substrate and hydrolyze it to AMP and pyrophosphate. Soluble forms of NPPases are activated by magnesium and strongly inhibited by Ap5A, which is also inhibitor of adenylate kinase.

Soluble NTPDases from CSF hydrolyze pyrophosphate bonds of diphosphonucleotides (ADP and GDP). Their catalytic activity requires presence of calcium ions and is partially inhibited by suramine.

In CSF we also found a new type of nucleotidase. That enzyme hydrolyzes ATP to ADP, requires either calcium or magnesium ions for activity, is insensitive to Ap5A and has an optimum pH 8.5. Maximal activity of this enzyme was found in CSF of patients with a stroke. Presence of phosphate groups in a products of the above enzyme excludes the participations of NPPases in this reaction. Therefore, it is an NTPDases-like soluble enzyme which prefers triphosphonucleotides as a substrate.

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