GILL PROTEIN-TURNOVER - COSTS OF ADAPTATION

Measurements of gill protein synthesis, and hence turnover, were great ly facilitated over the last decade by the application of ''flooding d ose'' methodology to non-mammalian species. Numerous studies show that in fish and aquatic invertebrates, gills are among the most active ti ssues with respect to protein turnover, this being true under a variet y oi environmental and nutritional conditions. The main components bei ng turned over in fish gills are probably collagen, primarily in the g ill arches, and epithelial cell proteins in the filaments, both arches and filaments having similar protein synthesis rates. Intriguingly, d ifferences are apparent between protein synthesis rates of adjacent ho lobranchs, the first (most anterior) being significantly more active t han the second or third, perhaps hinting at functional differences bet ween holobranchs. Experimental estimates of energetic costs for protei n synthesis, derived from cycloheximide treatment of isolated perfused gills, give a maximum value of 14 mmol O-2/g protein synthesized, whi ch is about double theoretical costs. Environmental stressors, such as heavy metals or acid/aluminum have variable effects on branchial prot ein turnover. Limited data suggest that zinc or acid exposure depresse s protein synthesis, whereas acid/aluminum increases it quite markedly . Calculations indicate that whereas effects within the gills may be s ubstantial, in terms of whole animal energetics, the costs of branchia l adaptation are likely to be small. COMP BIOCHEM PHYSIOL 119A;1:27-34 , 1998. (C) 1998 Elsevier Science Inc.