 The ~45kDa beta subunit has nine transmembrane segments which serve to couple the decarboxylation of the carboxybiotin to the translocation of Na+ from the cytoplasm to the periplasm.The small ~9kDa gamma subunit is an integral membrane protein with a single helix at the N-terminus, followed by a hydrophilic C-terminal domain which interacts with the alpha subunit.The gamma subunit is essential for the overall stability of the complex, and likely serves as an anchor to hold the alpha and beta subunits in place.