Distribution of ARF6 between membrane and cytosol is regulated by its GTPase cycle

The ADP-ribosylation factor (ARF) subfamily of small GTPases regulates intr acellular transport. Although much is known about how ARF1 regulates transp ort in the secretory pathways, regulation of the endocytic pathways by ARF6 remains less understood. In particular, whereas cycling of ARF1 between me mbrane and cytosol represents a major mechanism of regulating its function, this regulation has been questioned for ARF6, In this study, we found that ARF6 is distributed both on membranes and in the cytosol, Cytosolic ARF6 i s recruited to membranes in a GTP-dependent manner that is fundamentally si milar to ARF1. However, unlike ARF1, release of membrane-bound ARF6 to the cytosol requires hydrolysis of GTP that is sensitive to the level of magnes ium, These findings suggest that the GTPase cycle of ARF6 also regulates it s distribution between membrane and cytosol and that this form of regulatio n will also likely be important for the function of ARF6. Moreover, as ARF6 has little intrinsic ability to hydrolyze GTP, magnesium concentration mos t likely affects the release of membrane-bound ARF6 by altering the activit y of its GTPase-activating protein.