Inositol 5-phosphatase which may be involved in distinct membrane trafficking and signal transduction pathways. May mediate the inhibitory effect of Rac1 on endocytosis (By similarity). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-4,5-bisphosphate) + H2O = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4-phosphate) + phosphate Binds GRB2 and OMP25. Localizes at presynapse terminals in brain and at bundles of microtubules surrounding the nucleus in the elongating spermatids corresponding to the manchette. Translocates from the cytoplasm to membrane ruffles in a RAC1-dependent manner. Ubiquitously expressed, with the highest levels in heart and brain. Detected in cortex, cerebellum and olfactory bulb. Expressed in the testis. The C-terminal proline-rich region mediates binding to the SH3 domain-containing protein GRB2. Belongs to the synaptojanin family. In the central section; belongs to the inositol 1,4,5-trisphosphate 5-phosphatase family. Sequencing errors. Extended N-terminus.