ISOLATION AND PROPERTIES OF AN ATP TRANSPORTER FROM A STRAIN OF ASPERGILLUS-NIGER

A purified ATP transporter from Aspergillus niger did not show release or uptake for any of the nucleotides (ADP or UTP) except ATP. The rel ease and uptake did not result from non-specific binding, but appeared to be concentration-dependent processes. ATP was shown by a double-is otopic technique to be transported across membrane vesicles without de gradation. The ATP-transport protein was purified to near homogeneity from the membrane vesicles of a strain of A. niger and its apparent M- r was approximately 60 000. The purified protein showed the properties of a membrane-bound protein in that the carrier protein was shown, du ring the liposome-preparative process, to translocate from the aqueous phase into the lipid bilayer of the liposome, unlike the cytosolic pr otein glucose-6-phosphate dehydrogenase, which remained confined to th e aqueous compartment. Mycobacillin, a lipid-reactive antibiotic, was bound to the transport protein at a site other than the ATP-binding si te, leading to its enhanced release or uptake, which was very feeble i n absence of the antibiotic.