A soluble ATP-diphosphohydrolase (apyrase, EC 3.6.1.5) has been purified from potato tubers,Solanum tuberosum,to a specific activity of 10,000 μmol P_i/mg/min. The cDNA corresponding to the potato apyrase has been isolated and termed RROP1. The deduced amino acid sequence contains a putative signal sequence, two hydrophobic regions at the carboxy terminus, two potential Asn-linked glycosylation sites, and four regions in the amino-terminal half that we term ACR (apyrase conserved regions) 1–4 that are highly conserved in known apyrases and related enzymes: garden pea nucleoside triphosphatase,Toxoplasma gondiinucleoside triphosphate hydrolases, andSaccharomyces cerevisiaegolgi guanosine diphosphatase. A yeast 71.9-kDa hypothetical protein on chromosome V, aCaenorhabditis eleganshypothetical 61.3-kDa protein on chromosome III, and human CD39, a lymphoid cell activation antigen, also share the conserved ACR regions, but their ability to hydrolyze nucleotides has not been assessed.