Oxygen toxicity and carbon deprivation in Astasia longa

Abstract

The changes in metabolic activity of Astasia longa during oxygen treatment and carbon deprivation were examined. In many respects (growth, cell composition, and some enzymatic activities) the two treatments produce similar effects. Other parameters such as cellular respiration are affected differently. Oxygen treatment inhibits the ethanol-stimulated respiration but affects endogenous respiration very little. At the same time, the total alcohol dehydrogenase activity of the cell is increased at least 10-fold. In starved cells, the endogenous respiration is decreased parallel to the cellular content of carbohydrate reserves, but the ability of the cell to utilize ethanol stays constant. The NADH : cytochrome c oxidoreductase activity of the oxygen-treated cells is decreased by 70% whereas this activity is decreased less than 30% in starved cells. It is proposed that the inhibition of the NADH : cytochrome c oxidoreductase activity is the primary activity affected by oxygen treatment in both acetate- and ethanol-grown cells. The characteristic effects of oxygen treatment on ethanol-grown cells are probably the result of the combination of increased NAD-dependent alcohol dehydrogenase activity and decreased NADH : cytochrome c oxidoreductase activity. Such a modification of these two activities would tend to keep NAD in the reduced state and therefore limit cellular reactions which require oxidized NAD.