Microbody-marker Enzymes during Transition from Phototrophic to Organotrophic Growth in Euglena

Abstract

Transfer of Euglena gracilis Klebs Z cells from phototrophic to organotrophic growth on acetate results in derepression of the key enzymes of the glyoxylate cycle, malate synthase and isocitrate lyase, which appear coordinately regulated. The derepression of malate synthase and isocitrate lyase was accompanied by increased specific activities of succinate dehydrogenase, fumarase, and malate dehydrogenase, but hydroxypyruvate reductase activity was unaltered.Isolation of organelles from broken cell suspensions of cells grown heterotrophically on acetate was achieved by isopycnic centrifugation on sucrose gradients. Peaks of mitochondrial enzymes were obtained at equilibrium densities of 1.22 g cm(3) and 1.16 g cm(3), and although significant differences in the distribution of tricarboxylic acid cycle enzymes between these two peaks were not recorded adenosine triphosphatase activity was detected only in the less dense fraction (1.16 g cm(3)) showing this contained damaged mitochondria. The peak of particulate glyoxylate cycle enzymes was at an equilibrium density of 1.25 g cm(3), this being the same as that for glycolate pathway enzymes from phototrophic cells. Citrate synthase, isocitrate lyase, malate synthase, and malate dehydrogenase were all present in this fraction so it was concluded that Euglena glyoxysomes contain a complete glyoxylate cycle.