Fig. 3. Dehydroascorbate (DHA) protects mitochondrial respiration with malate as a substrate from inhibition by sulfide. Oxygen consumption rates of mitochondria from the body wall tissue of Arenicola marina as a function of time. Additions (indicated by arrows) were 8 mmoll^–1 malate and 1 mmoll^–1 ADP. Subsequently 1 mmoll^–1 DHA was added only to the assay shown by the black line at the time marked with X. The injection of 50 µmoll^–1 sulfide inhibited malate respiration in the absence of DHA (gray line) and, by contrast, stimulated the oxygen consumption rate in the presence of DHA (black line).