Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

Extracellular inorganic pyrophosphate (PPi) is important in the regulation of mineralisation of bone, and in the pathogenesis of chondrocalcinosis, an arthritic disease in which calcium pyrophosphate dihydrate crystals form in articular cartilage. Nucleoside-triphosphate pyrophosphatase, which catalyses the formation of PPi, was previously observed at the surface of human articular chondrocytes in culture. A similar enzyme has been identified in osteoblast-like human bone cells in culture, and is active towards purine and pyrimidine nucleoside triphosphates. The enzyme has high affinity for ATP and is located on the cell surface, and thus could serve in the generation of extracellular PPi. Moreover, no other mechanism for the catabolism of small amounts of exogenous ATP is present in human bone cells. Further evidence for ecto-nucleoside-triphosphate pyrophosphatase serving in the generation of extracellular PPi in articular cartilage and bone was obtained by studying the ability of alternative substrates (which do not yield PPi) to inhibit generation of PPi from ATP. In both articular chondrocytes and bone cells, the enzyme exhibited an apparent preference for ATP over dinucleotide and phosphodiester substrates. Some potential inhibitors of the enzyme activity were also studied in both cell types. ADP moderately inhibited the activity but two bisphosphonate drugs were only slightly inhibitory.

Original publication




Journal article


Biochim biophys acta

Publication Date





310 - 317


Bone Matrix, Cartilage, Articular, Cells, Cultured, Diphosphates, Extracellular Matrix, Humans, Pyrophosphatases, Substrate Specificity