Possesses GTPase activator activity towards RAB32, RAB33B and RAB38. Regulates the trafficking of melanogenic enzymes TYR, TYRP1 and DCT/TYRP2 to melanosomes in melanocytes by inactivating RAB32 and RAB38. Inhibits RAB32 and RAB38 activation both directly by promoting their GTPase activity and indirectly by disrupting the RAB9A-HPS4 interaction which is required for RAB32/38 activation (PubMed:26620560). Interacts with RAB4A, RAB11A, RAP1A, RAP1B, RAP2A and RAP2B. No interaction with RAB27A. Interacts with RAB9A (By similarity). Melanosomal localization is mediated by RAB9A. Widely expressed. The Rab-GAP TBC domain possesses GTPase activator activity. Belongs to the RUTBC family.