inositol hexakisphosphate & diphosphoinositol-pentakisphosphate kinase 2 (insP6 & PP-IP5 kinase 2, PP-IP5 kinase 2, hsVIP2, histidine acid phosphatase domain-containing protein 1, HISPPD1, KIAA0433, PPIP5K2, VIP2)

Function

• bifunctional inositol kinase
• catalyzes formation of diphosphoinositol pentakisphosphate (insP7 or PP-insP5) & bi-diphosphoinositol tetrakisphosphate (insP8 or PP2-insP4) converts inositolitol hexakisphosphate (insP6) to insP7
• also able to convert insP7 to insP8
• probably specifically mediates formation of 4PP-insP5 & 6PP-insP5 insP7 isomers but not of 5PP-IP5 insP7 isomer

ATP + 1D-myo-inositol hexakisphosphate
                 <-->
ADP + 5-diphospho-1D-myo-inositol (1,2,3,4,6)pentakisphosphate

ATP + 1D-myo-inositol 1,3,4,5,6-pentakisphosphate
                 <-->
ADP + diphospho-1D-myo-inositol tetrakisphosphate
(isomeric configuration unknown)

ATP + 1D-myo-inositol 5-diphosphate pentakisphosphate
                 <-->
ADP + 1D-myo-inositol bisdiphosphate tetrakisphosphate
     (isomeric configuration unknown)

Kinetic parameters:

• KM=0.13 uM for insP6
• KM=0.19 uM for insP7
• Vmax=0.39 nmol/min/mg enzyme with insP6 as substrate
• Vmax=1.38 nmol/min/mg enzyme with insP7 as substrate

Structure

• belongs to the histidine acid phosphatase family. VIP1 subfamily
• although related to histidine acid phosphatases, it lacks the conserved active sites, suggesting that it has no phosphatase activity

Compartment

cytoplasm, cytosol

Alternative splicing

named isoforms=2

More general terms

• kinase or ATP-phosphotransferase
• phosphoprotein

Database

• UniProt: http://www.uniprot.org/uniprot/O43314.html