Abstract
Differential centrifugation and Percoll-gradient centrifugation of protoplast lysates of suspension-cultured cells of sycamore (Acer pseudoplatanus L.) yielded pure amyloplasts. Contamination of the final amyloplast preparation by foreign compartments was assessed by measuring marker enzyme activities. The activity of alkaline pyrophosphatase was taken as a 100% plastid marker; relative to this marker, mitochondria (cytochrome c oxidase) averaged 0.34%, microbodies (catalase) 0.61%, and cytosol (alcohol dehydrogenase) 0.09%. Enzymatic activities of the glycolytic, gluconeogenic, pentose phosphate and the starch degradation pathways were found to be present in these amyloplast extracts in appreciable amounts. But the pyrophosphate-dependent phosphofructokinase and phosphoglyceromutase were judged to be essentially absent from amyloplasts because the activities of these enzymes were not enriched above the level of contaminating enzymatic activities in the amyloplast fractions. Additionally, the in vitro activities of starch phosphorylase, ATP dependent phosphofructokinase, NAD dependent glyceraldehyde-3 phosphate dehydrogenase, and glucose-6 phosphate dehydrogenase did not seem to support carbon fluxes from starch to triose phosphates as calculated from the rate of starch disappearance during carbon starvation of the cells. These results provide additional, indirect evidence for the recently emerged view that, in addition to the well known phosphate-triosephosphate translocator, another hexose phosphate and possibly also an ATP/ADP translocating system play major roles in nongreen plastids.