This family is the probable catalytic subunit of the GTPase activating protein that has specificity for Rab3 subfamily (RAB3A, RAB3B, RAB3C and RAB3D). It is likely to convert active Rab3-GTP to the inactive form Rab3-GDP. Rab3 proteins are involved in regulated exocytosis of neurotransmitters and hormones. The Rab3 GTPase-activating complex is a heterodimer composed of RAB3GAP and RAB3-GAP150. This complex interacts with DMXL2.