Immunochemical Analysis Shows That an ATP/ADP-Translocator Is Associated with the Inner-Envelope Membranes of Amyloplasts from Acer pseudoplatanus L.

Abstract

Pure preparations of intact amyloplasts and chloroplasts, free from mitochondrial contamination, were isolated from cultured cells of the white-wild and green-mutant lines of sycamore (Acer pseudoplatanus L.), respectively. A specific rabbit antiserum against yeast mitochondrial cytochrome c₁ only cross-reacted with mitochondrial membranes from the white-wild sycamore cells. The outer and inner envelope-membranes of the two plastid-types were isolated and subsequently analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis to characterize polypeptide patterns in each fraction. Analysis by immunoblotting clearly showed that antiserum against the 29-kilodalton inorganic orthophosphate translocator isolated from pea chloroplasts cross-reacted with a 31-kilodalton polypeptide residing in the inner-envelope membranes from both sycamore chloroplasts and amyloplasts. In contrast, antiserum against the ADP/ATP-translocator isolated from mitochondria of Neurospora crassa yielded a positive signal with a 32-kilodalton polypeptide in the inner-membranes isolated from amyloplasts, but not green-mutant chloroplasts. We propose that this 32-kilodalton polypeptide in the amyloplast envelope is a putative ATP/ADP-translocator and its possible functional significance is discussed.