Abstract
The activity of the electron transport system (ETS) in D. magna and the crayfish Orconectes propinquus was estimated by measuring NADH-, succinate- and NADPH-cytochrome c reductase. The activity of the total ETS was 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 was highest in crayfish gill when NADH or succinate was used as substrate, and highest in crayfish hepatopancreas when NADPH was used. Km for NADH, NADPH and cytochrome c were 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.