Biosynthesis and Cellular Distribution of the Two Superoxide Dismutases of Dactylium dendroides

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Abstract
The synthesis and subcellular localization of the 2 superoxide dismutase [EC 1.15.1.1] of D. dendroides were studied in relation to changes in Cu and Mn availability. Cultures grew normally at all medium Cu concentrations used (10 nM-1 mM). In the presence of high (10 .mu.M) Cu, Mn was poorly absorbed in comparison to the other metals in the medium. Cells grown at 10 nM Cu exhibited a 3.5-fold increase in Mn content, while the concentration of the other metals remained constant. Cultures grown at 10 nM Cu or more had 80% Cu/Zn enzyme and 20% mangani enzyme; the former was entirely in the cytosol, and the latter was mitochondrial Removal of Cu from the medium resulted in the decreased Cu/Zn superoxide dismutase synthesis with a concomitant increase in the mangani enzyme such that total cellular superoxide dismutase activity remained constant. The mangani enzyme in excess of the 20% was present in the non-mitochondrial fraction. The mitochondria show no variability with respect to superoxide dismutase content, whereas the soluble fraction varies from 100-13% Cu/Zn superoxide dismutase. Copper-starved cells that were synthesizing predominantly mangani superoxide dismutase could be switched over to mostly Cu/Zn superoxide dismutase synthesis by supplementing the medium with Cu during growth. Immunoprecipitation experiments suggest that the decrease in Cu/Zn activity at low Cu concentration is a result of decreased synthesis of that protein rather than the production of an inactive apoprotein.

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