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Articles

Nutritional Regulation of Organelle Biogenesis in Euglena^1,2

INDUCTION OF MICROBODIES

School of Life Sciences, University of Nebraska, Lincoln, Nebraska 68588

Exposure of dark grown resting Euglena to ethanol produced a transient increase in the specific activity of the glyoxysomal enzyme malate synthase. Enzyme specific activity increased during the first 24 hours of ethanol treatment and then declined. Light exposure or malate addition failed to increase enzyme specific activity. The increase and decrease in enzyme specific activity represented changes in the amount of active enzyme. In both wild type cells and the plastidless mutant W₃BUL, enzyme levels were always higher in the dark than in the light.

The specific activity of the peroxisomal enzyme glycolate dehydrogenase began to increase 24 hours after dark grown resting Euglena were exposed to light. Ethanol, but not malate, prevented the increase and promoted a decrease in glycolate dehydrogenase levels. Cycloheximide produced a decline in enzyme levels similar to the decline produced by ethanol addition. Glycolate dehydrogenase was present in the plastidless mutant W₃BUL indicating that it is coded in the nucleus and synthesized on cytoplasmic ribosomes. Streptomycin, a specific inhibitor of chloroplast protein synthesis and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthetic CO₂ fixation, inhibited the photoinduction of glycolate dehydrogenase while having no effect on the photoinduction of NADP dependent glyceraldehyde-3-phosphate dehydrogenase, another light induced, nuclear coded, cytoplasmically synthesized enzyme. Taken together, these results suggest that microbodies are continually synthesized in resting Euglena and their enzyme complement is determined through substrate induction of glyoxysomal and peroxisomal enzymes.

⁴ To whom reprint requests should be addressed.

¹ This research was supported by National Institutes of Health Grant GM26994, Biomedical Support Grant RR-07055, and funds from the Research Council, University of Nebraska.

² This work was taken from a dissertation submitted to the graduate faculty of the University of Nebraska by M. A. H. in partial fulfillment of the requirements for the PhD degree.