ENPP1 and ankylosis: MVs also house various ion-motive ATPases [48] providing Pi, as well as progressive ankylosis protein [45], a PPi transporter from the lumen of MVs or from cells to the extracellular medium, and ectonucleotide pyrophosphatase phosphodiesterase 1 (NPP1) [45,49], which produce PPi from ATP or UTP.