Acts as a GTPase-activating protein (GAP) for tubulin in concert with tubulin-specific chaperone C, but does not enhance tubulin heterodimerization. Acts as a GTPase-activating protein. May act as guanine nucleotide dissociation inhibitor towards ADP-ribosylation factor-like proteins (By similarity). Detected predominantly at the plasma membrane of rod and cone photoreceptors. Not detected in the nucleus. Myristoylated on Gly-2; which may be required for membrane targeting. Palmitoylated on Cys-3; which may be required for plasma membrane targeting. Belongs to the TBCC family.