Arginine metabolism of the Antarctic Bivalve Laternula elliptica (King & Broderip, 1831): an ecophysiological approach

The potential aerobic ATP-generating pathway and the argininolytic capacity of the Antarctic bivalve Laternula elliptica in its main tissues were measured by the specific activity of the enzymes malate dehydrogenase (MDH), citrate synthase (CS) and arginase. The kidney showed the major potential for aerobic ATP-generating pathway and argininolytic capacity. High levels of CS and MDH activities indicated that renal tissue can be involved in activities that require a lot of energy such as excretion of metabolic end products, amino acids catabolism or even gluconeogenic activities related to inter-tissue metabolism. The fact that kidneys are the main site for arginase activity is very unusual for mollusks and could be related to the living habits of L. elliptica. Genetic expression of the L. elliptica renal arginase could be controlling the levels of L-arginine and forming urea in the excretory organ, which may not have its physiological functions directly affected by the seasonal retraction of its siphons. Compared to the bivalve Dreissena polymorpha, renal arginase of L. elliptica is more resistant to inhibition by copper and cadmium. This could be related to naturally high levels of these metals in the Antarctic marine environment and its bioaccumulation in the renal tissue of L. elliptica, as a probable advantage to its environmental adaptation. Different from other Antarctic animals that feed on Krill, the arginase of L. elliptica is much more sensitive to fluoride inhibition. However, diet composition of L. elliptica would be expected to be variable site to site and its high sensitivity to fluoride inhibition may be a matter of concern in areas near ornithogenic soils subjected to ice-melting processes.