Controlling proteome degradation in Daphnia pulex.

An attempted proteomic study of Daphnia pulex response to sodium chloride exposure revealed an unexpected result: very strong proteome degradation previously observed in D. pulex is halted when animals have been exposed to elevated salinity prior to protein extraction. Further characterization of conditions controlling proteome degradation shows that the proteolytic factor(s) is/are present in an active form under chemically denaturing conditions in extract from control "normal/healthy" animals, and can be negatively regulated by prior in vivo salinity exposure of animals or inhibited by post-homogenization heating of samples. We interpret these data as evidence for salinity-induced inhibition of proteolysis in Daphnia.