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PiUS (Pi uptake stimulator) is an inositol hexakisphosphate kinase
M J Schell1, A J Letcher, C A Brearley
1Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK.
Abstract:
A cDNA cloned from its ability to stimulate inorganic phosphate uptake in Xenopus oocytes (phosphate uptake stimulator (PiUS)) shows significant similarity with inositol 1,4,5-trisphosphate 3-kinase. However, the expressed PiUS protein showed no detectable activity against inositol 1,4,5-trisphosphate, nor the 1,3,4,5- or 3,4,5, 6-isomers of inositol tetrakisphosphate, whereas it was very active in converting inositol hexakisphosphate (InsP(6)) to inositol heptakisphosphate (InsP(7)). PiUS is a member of a family of enzymes found in many eukaryotes and we discuss the implications of this for the functions of InsP(7) and for the evolution of inositol phosphate kinases.