Characterization of the ATP-dependent proton pump of clathrin-coated vesicles.

The abbreviations used are: MES, 2-(N-morpholino)ethanesulfonic acid; NBD-Cl, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole; HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; EGTA, ethylene glycol bid@-aminoethyl ether)-N,N,N',N'-tetraacetic acid.(Na+,K+)-ATPase was purified from canine kidney by the procedure of Jorgensen ( 19) and had a specific activity of approximately 10 pmol of ATPlminjmg of protein at 23 "C.K+ is unlikely to activate dephosphorylation of the coated vesicle proton pump (as it does with the (Na+,K+)-ATPase) since K+ is not required for ATPase activity (10) and @Rb+ (a K+ analog) is Dot transported during ATP-dependent proton uptake by the coated vesicles (see below).