Meeting Abstract

P1.61  Wednesday, Jan. 4  Carbonic anhydrase induction in the euryhaline blue crab, Callnectes sapidus, during low salinity acclimation is rate-limited by protein synthesis MITCHELL, Reed T*; PINHO, Breanna SH; HENRY, Raymond P; Auburn University; Auburn University; Auburn University

An essential component of the ability of the marine blue crab, Callinectes sapidus, to survive in low-salinity environments is an increase in cytoplasmic carbonic anhydrase (CA) activity in the posterior, ion-regulating gills. This is accomplished via a two-step mechanism involving rapid gene activation followed by synthesis of new enzyme. Upon transfer from 35 ppt to low salinity, relative expression of cytoplasmic CA mRNA (CAc) increases 100-fold at 12 hr; however, it is not until 96 hr that new acclimated levels of CA activity are reached. This delay in activity suggests that protein synthesis, not gene activation, is the rate-limiting step. To further test this we measured both CAc expression and CA activity in crabs acclimated to 35 ppt and transferred to 22 ppt, and in crabs transferred from 22 to 10 ppt. In the 22 ppt transfer, crabs did not show an increase in CA activity until 48 hr post transfer. In the 10 ppt group CA activity did not rise until 24 hrs, despite high levels of gene expression at 22 ppt. These results demonstrate that despite the priming of the CA induction mechanism at 22 ppt, increases in CA activity still take on the order of days to occur. This may be due to necessary post-translational modifications such as the insertion of a zinc atom into the active site of the enzyme. Preliminary testing of zinc as a limiter of CA activity has yet to yield conclusive results.