Fig. 2. Original recordings of (A) oxygen concentrations (µmoll^–1) and (B) ATP concentration (µmoll^–1) calculated from the NADPH absorbance at 340 nm in mitochondrial suspensions from body wall tissue of Arenicola marina. (A) Effect of redox-competent molecules on oxygen consumption with sulfide as a substrate. The assays contained 0.45 mg ml^–1 mitochondrial protein and either 1 mmoll^–1 dehydroascorbate (DHA) (trace 2) or 2.5 mmoll^–1 GSH plus 2.5 mmoll^–1 ascorbate (trace 3). The reactions were started by the addition of 50 µmoll^–1 sulfide. In the presence of DHA, the oxygen consumption rate could be stimulated by ADP. (B) Activation of ATP production with 50 µmoll^–1 sulfide as a substrate by DHA. The amount of mitochondrial protein present was 0.16 mg ml^–1. Additions are indicated by arrows.