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.