Dephosphorylation of 1D-myo-inositol 1,4-bisphosphate in rat liver.
Dephosphorylation of 1D-myo-inositol 1,4-bisphosphate [Ins(1,4)P2] in rat liver is catalysed by a cytosolic phosphatase that removes the 1-phosphate group. The Km for Ins(1,4)P2 is approx. 17 microM. Li+ (100 mM) causes 50% inhibition of Ins(1,4)P2 phosphatase activity when activity is measured at the very low substrate concentration of 10 nM, but on raising the substrate concentration to 100 microM there is a greater than 10-fold increase in sensitivity to Li+, suggesting that Li+ acts mainly, but not entirely, as an uncompetitive inhibitor of Ins(1,4)P2 phosphatase. In addition, rat liver cytosol shows Li+-sensitive phosphatase activity against 1D-myo-inositol 1-,3- and 4-monophosphates. The Ins(1,4)P2 1-phosphatase and inositol monophosphatase activities all share an apparent Mr of 47 x 10(3), as determined by gel-filtration chromatography. However, the Ins(1,4)P2 1-phosphatase is more sensitive to inactivation by heat, and can be separated from inositol monophosphatase activity by anion-exchange chromatography. We conclude that rat liver cytosol contains an Ins(1,4)P2 1-phosphatase that is distinct from, but in many ways similar to, inositol monophosphatase.
Morris
A J
AJ
Department of Biochemistry, University of Birmingham, U.K.
Storey
D J
DJ
Downes
C P
CP
Michell
R H
RH
D000818:Animals; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000201:enzymology; D007295:Inositol Phosphates / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology; D013403:Sugar Phosphates / Q000378:metabolism*
D007295:Inositol Phosphates; D013403:Sugar Phosphates; C044259:inositol 1,4-bis(phosphate); D008094:Lithium; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase; C053087:inositol-1,4-bisphosphate 1-phosphatase