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 mumol 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 gondii nucleoside triphosphate hydrolases, and Saccharomyces cerevisiae golgi guanosine diphosphatase. A yeast 71.9-kDa hypothetical protein on chromosome V, a Caenorhabditis elegans hypothetical 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.