The phosphate carrier of the inner mitochondrial membrane has been purified
from potato tuber in a nearly homogenous form and characterized after reco
nstitution into liposomes. The mitochondrial membrane was solubilised by Tr
iton X-114 in the presence of cardiolipin and the soluble fraction was chro
matographied on hydroxylapatite. The flow-through fractions were collected
and analyzed by SDS-gel electrophoresis. In some fractions, a single protei
n band of M-r = 35 kDa was found. This protein was reconstituted into phosp
hatidylcholine vesicles and its capability to transport phosphate was measu
red by phosphate-phosphate exchange. A maximum velocity of 28.1 mu mol min(
-1). (mg of protein)(-1) was detected. Phosphate transport was sensitive to
mersalyl and N-ethylmaleimide. On the other hand, no proton transport was
apparent in these proteoliposomes, unlike to what was seen with Similar hyd
roxylapatite-purified fractions obtained after solubilization of the membra
ne by decyl-pentaoxyethylene ether, which contained several polypeptides. T
hus the phosphate carrier is distinct from the uncoupling protein (UCP) fam
ily and its behavior shows that not all anion carriers are able to act as U
CPs, (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserve
d.