Ecto-Nucleotidases

Abstract

Ecto-nucleotidases are cell surface-located enzymes which catalyze extra-cellular nucleotide hydrolysis. An extracellular hydrolysis pathway for nucleotides has been detected in essentially all tissues and also in a large variety of cell culture systems. Its general features include the following:

• 1. Nucleoside 5′-triphosphates are sequentially metabolized to the nucleoside with nucleoside 5′-diphosphate and nucleoside 5′-monophosphate appearing as intermediate products. The nucleoside may then be further deaminated to inosine by adenosine deaminase (Franco et al. 1997).

• 2. Not only ATP, ADP, and AMP but essentially all physiologically occurring purine and pyrimidine nucleotides are hydrolyzed.

• 3. Extracellular hydrolysis of nucleotides is not inhibited by known inhibitors of intracellular ATPases such as P-type, F-type, and V-type ATPases.

• 4. Nucleotide hydrolysis depends on divalent cations, generally millimolar concentrations of either Ca²⁺ or Mg²⁺.

• 5. Nucleotide hydrolysis has an alkaline pH optimum.

• 6. A major function of the extracellular enzyme chain appears to be the termination of the physiological action of nucleotides released from cells.

To date no information is available as to whether the hydrolysis of ATP is used to drive energy-dependent processes (for reviews of the earlier work see Arch and Newsholme 1978; Fox 1978; Pearson 1985; Dhalla and Zhao 1988; Ziganshin et al. 1994a; Plesner 1995; Sarkis et al. 1995; Beaudoin et al. 1996; Zimmermann 1996a,b; Plesner et al. 1997; Zimmermann and Pearson 1998).