Intracellular localization of CO 2 metabolism enzymes in cactus phylloclades

Abstract

Chloroplasts were prepared from cactus, Opuntia Ficus- indica Mill., phylloclades by aqueous and nonaqueous techniques in order to localize CO 2 metabolism enzymes. Phosphoenolpyruvate carboxylase, malate dehydrogenase, malic enzyme, glutamic-oxaloacetic transaminase, and glucose-6-phosphate dehydrogenase were shown to be associated with the purified chloroplasts. Malic dehydrogenase, malic enzyme, glutamic-oxaloacetic transaminase and glucose-6-phosphate dehydrogenase were associated with mitochondria purified by sucrose density gradients. Recovery of enzymic activity from chloroplasts prepared by carbon tetrachloride-hexane density gradient centrifugation was significantly better than plastids prepared by sucrose density gradient centrifugation. Because P-enolpyruvate carboxylase, malic dehydrogenase, and malic enzyme activities were associated with chloroplasts, CO 2 metabolism mediated by these enzymes must be associated with chloroplast metabolism.