Excretion of free amino acids and ammonia by Daphnia magna was measured by examining in vitro changes in concentration of the two forms of nitrogen over 4–6 h. Mean weight-specific amino acid release rate (± SE) for 32 healthy daphnids was 0.13 ± 0.03 nmol (mg dry wt)−1∙h−1 as compared with a mean ammonia excretion rate of 21 ± 2 nmol (mg dry wt)−1∙h−1. Net removal from solution was observed when low levels of amino acids (2 nmol/8 mL) were added to the water before incubation, indicating that measured net release rates could be reduced by amino acid uptake. Toxic levels (0.5 mg∙L−1) of lead, arsenic, Kepone, toxaphene, malathion, or pentachlorophenol, added to stress the animals, did not significantly affect release rates of amino acids or ammonia, but the addition of copper (as CuSO4) increased amino acid release by daphnids and hindered microbial removal of amino acids from incubation waters. Amino acids released from copper-exposed animals were similar in composition to those in intracellular amino acid pools of D. magna, suggesting that diffusion across cell membranes may have been the mechanism for amino acid release.Key words: amino acids, ammonia, cladocera, contaminants, copper, Daphnia, excretion, free amino acids, stress, zooplankton
In a previous communication' a derivative of the postulated rearrangement p r o d u~t~,~ from the triphenylmethyl ether of o-cresol was reported.However, the synthetic a-2-methoxyphenyl-fl, p,-@-triphenylethane possessed a lower m. p. oi of reactions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.