| Abstrakt: |
Diadenosine polyphosphates (Apn As) act as extracellular signaling molecules in a broad variety of tissues. They were shown to be hydrolyzed by surface-located enzymes in an asymmetric manner, generating AMP and Apn-1 from Apn A. The molecular identity of the enzymes responsible remains unclear. We analyzed the potential of NPP1, NPP2, and NPP3, the three members of the ecto-nucleotide pyrophosphatase/phosphodiesterase family, to hydrolyze the diadenosine polyphosphates diadenosine 5′,5′′′-P1 ,P3 -triphosphate (Ap3 A), diadenosine 5′,5′′′-P1 ,P4 -tetraphosphate (Ap4 A), and diadenosine 5′,5′′′-P1 ,P5 -pentaphosphate, (Ap5 A), and the diguanosine polyphosphate, diguanosine 5′,5′′′-P1 ,P4 -tetraphosphate (Gp4 G). Each of the three enzymes hydrolyzed Ap3 A, Ap4 A, and Ap5 A at comparable rates. Gp4 G was hydrolyzed by NPP1 and NPP2 at rates similar to Ap4 A, but only at half this rate by NPP3. Hydrolysis was asymmetric, involving the α,β-pyrophosphate bond. Apn A hydrolysis had a very alkaline pH optimum and was inhibited by EDTA. Michaelis constant (K m ) values for Ap3 A were 5.1 µm, 8.0 µm, and 49.5 µm for NPP1, NPP2, and NPP3, respectively. Our results suggest that NPP1, NPP2, and NPP3 are major enzyme candidates for the hydrolysis of extracellular diadenosine polyphosphates in vertebrate tissues. [ABSTRACT FROM AUTHOR] |
