Effect of Hydrogen Sulfide Loading on the Activity of Energy Metabolism Enzymes and the Adenylate System in Tissues of the Anadara kagoshimensis Clam

Species with a high resistance to hypoxia are usually characterized by an increased H2S tolerance of hydrogen sulfide; however, high anaerobic potential cannot be the only explanation for survival in an environment with elevated concentrations of sulfides. The activity of oxidoreductases, as well as parameters of adenylate system were studied in the tissues of hypoxia/anoxia-tolerant clam Anadara kagoshimensis (Tokunaga, 1906) under conditions of experimental H2S loading (HSL). Adult specimens with a shell height of 26–38 mm are used. The control group of clams is kept in an aquarium with an oxygen concentration of 7.0–7.1 mg/L (normoxia). The experimental group is exposed to the effect of HSL created by dissolving sodium sulfide (H2S donor) in water to a final concentration of 6 mg S2–/L; exposure time is 24 h. After the first day of the experiment, the level of O2 in water is 1.8 mg/L and there is no hydrogen sulfide. Some of the clams are exposed to repeated hydrogen sulfide loading (second day of the experiment), and Na2S is introduced to a final concentration of 9 mg S2–/L; by the end of the second day, 1.9 mg S2–/L and trace concentration of O2 (0.03 mg/L) are registered. In the first days of HSL, a high activity of malate dehydrogenase (MDH) against the background of a significant suppression of the activity of lactate dehydrogenase (LDH) and an increase in the values of MDH/LDG index persists; this reflects a strengthening of anaerobic processes in the tissues of anadara with relatively high concentrations of О2 in water (1.8 mg/L). After the second day of HSL, the activity of oxidoreductases in the clam tissues does not change when compared with the first day; however, the value of adenylate energy charge (AEC) persists against the background of a relative decrease in [ATP]. The retention of AEC indicates the ability of the anadara to exist under conditions of hydrogen sulfide contamination and acute forms of hypoxia/anoxia.