Energy metabolism of arthropods and mollusks during environmental and functional anaerobiosis

During environmental anaerobiosis, when the whole organism is exposed to anoxic conditions caused by external, physical factors in the microhabitat, arginine phosphate, glycogen, and aspartate (only mollusks) are the substrates for the metabolism. Main end products formed are lactate (Crustacea, Xiphosura, some Gastropoda and Bivalvia), alanine, succinate, and the volatile fatty acids, propionate and acetate (most Gastropoda and most Bivalvia). Because of reduction of the overall metabolism in bivalves, utilization and production rates of substrates and end products, respectively, are low. They are generally faster in Crustacea, which do not reduce their metabolism. During functional anaerobiosis, when the muscle tissue becomes anoxic because of increased work done by the animal, energy is derived from arginine phosphate and glycogen. The main end products formed are lactate (Crustacea), octopine (active Gastropoda and Bivalvia), and strombine/alanopine (some gastropod species). Utilization rates of the phosphagen and production rate of lactate and opines are sometimes more than 500‐fold higher than during environmental anaerobiosis. These strong variations in the glycolytic flux are probably regulated by the influence of the phosphagen and adenylates on regulatory enzymes and by the NADH/NAD ratio.