WILLETT, C. S.*; BURTON, R. S.; Univ. of North Carolina, Chapel Hill; Scripps Institution of Oceanography: Molecular genetics of osmoregulation: Regulation of free amino acid accumulation in copepods under hyperosmotic stress

The intracellular accumulation of free amino acids is a common response of diverse organisms to increasing salinities in the extracellular environment. In crustaceans, proline is most often the dominant free amino acid accumulated in response to hyperosmotic stress. In the euryhaline copepod Tigriopus californicus the synthesis of proline from its metabolic precursors is tightly regulated by environmental salinities. Previous work has suggested that the enzyme ∆1-pyrroline-5-carboxylase synthase (P5CS) lies at the key regulatory point in this pathway. We have characterized the gene encoding this enzyme in T. californicus and monitored its expression under hyperosmotic stress. The abundance of the transcript of this gene does not increase in response to hyperosmotic stress. Two additional enzymes in the proline synthesis pathway have also been examined: Neither glutamate dehydrogenase nor ∆1-pyrroline-5-carboxylase reductase shows increased transcript abundance or enzyme activity under hyperosmotic stress. This work suggests that if P5CS is indeed the key enzyme in proline regulation under hyperosmotic stress in T. californicus, control must be mediated by either translational control or post-translational modification of this enzyme.