Characterization of a purified co-transporting protein

1. A protein of mol weight 280,000 D was isolated and purified by means of a furosemide affinity gel. 2. Binding of 3H-bumetanide suggests that the protein is identical to the Na-K-2Cl co-transporter. 3. If the protein was reconstituted into a planer lipid bilayer, a Cl- -channel of 12 pS and a K+-channel of about 130 pS was observed. 4. Whether these channel activities represent a co-purification of channel proteins or whether the channel activity originates from the purified and reconstituted co-transporting protein itself was discussed.