Electron transport system activity in Daphnia and crayfish

Abstract

The activity of the electron transport system (ETS) in Daphnia magna and the crayfish Orconectes propinquus was estimated by measuring NADH-, succinate-, and NADPH-cytochrome c reductase. The activity of the total ETS was also measured by following NADH oxidation, and by measuring the rate of cytochrome c reduction upon addition of cyanide after a steady state between cytochrome c reductase (EC 1.6.99.3) and cytochrome oxidase (EC 1.9.3.1) had been reached. ETS activity is highest in crayfish gill when NADH or succinate is used as substrate, and highest in crayfish hepatopancreas when NADPH is used. Michaelis–Menten constants for NADH, NADPH, and cytochrome c are comparable with some of the lower values reported for mammalian systems. The usefulness of the ETS assay in the study of toxic substances is discussed.