ectonucleoside triphosphate diphosphohydrolase 8 (NTPDase 8, NTPDase8, E-NTPDase 8, ENTPD8)

Function

• canalicular ectonucleoside NTPDase responsible for the main hepatic NTPDase activity
• ectonucleoside NTPDases catalyze hydrolyzis of gamma & beta-phosphate residues of nucleotides, playing a role in concentration of extracellular nucleotides
• has activity toward ATP, ADP, UTP & UDP, but not toward AMP
• not inhibited by ARL 67156

Kinetic parameters:

• KM=81 uM for ATP
• KM=137 uM for ADP
• KM=480 uM for UTP
• KM=241 uM for UDP
• Vmax=790 nmol/min/mg enzyme with ATP as substrate
• Vmax=163 nmol/min/mg enzyme with ADP as substrate
• Vmax=1100 nmol/min/mg enzyme with UTP as substrate
• Vmax=110 nmol/min/mg enzyme with UDP as substrate

ATP + 2 H2O <--> AMP + 2 phosphate

Cofactor: Ca+2 (putative)

Structure

• transmembranous domains are involved in regulation of enzyme activity
• belongs to the GDA1/CD39 NTPase family
• N-glycosylated

Compartment

cell membrane

Alternative splicing

named isoforms=2

More general terms

• membrane protein

Database

• UniProt: http://www.uniprot.org/uniprot/Q5MY95.html