The identification of a membrane-bound myo-inositol 1-phosphatase in rat brain, liver, and testes.

A membrane-bound myo-inositol 1-phosphatase has been solubilized and partially purified from rat tissues. This particulate enzyme was detected in brain, liver and testis and certain physicochemical and enzymological properties were examined. Previously this major enzyme of the inositol signaling system was considered strictly cytosolic. The ratio of activity in the membrane form was approximately one-eighth of the activity found with the cytosolic fraction. The molecular weight of this phosphatase was found to be 59,000 by gel filtration chromatography and a subunit molecular weight of 29,000 by Western blot analysis, values comparable to the cytosolic form. This phosphatase cleaves both D- and L- myo-inositol 1-phosphates which originate from two different cellular pathways and is inhibited by lithium ions. Polyclonal antibodies were raised against homogeneous testicular cytosolic myo-inositol 1-phosphatase and cross-reacted with this membrane form as determined by western blot analysis showing immunological identity.