Biotinylation of βENaC. Kidneys from rats on a low-Na diet were perfused with or without biotin. Lanes were loaded with 40 μg of total membrane protein or 20 μl of eluate from the neutravidin beads. Total membranes from whole kidney had a predominant stained band at ∼90 kD. Fainter staining at the same molecular mass was observed in eluates from biotinylated kidneys. No staining was detected in eluates from nonbiotinylated kidneys.