Enzymatic capacities for beta-oxidation of fatty fuels are low in the gillof teleost fishes despite presence of fatty acid-binding protein

A variety of circulating fuels can support the work of the teleost gill. Pr evious work indicates, however, that unlike other aerobic tissues from tele osts, the gill may have a limited capacity to oxidize fatty fuels. We deter mined capacities for catabolism of carbohydrate, fatty acids, and amino aci ds in four species of temperate marine or euryhaline teleosts representing distinct lineages. In addition, we assessed the capacity for fatty acid oxi dation in the gill from an Antarctic species. Activities of rate-limiting o r regulatory enzymes from pathways of energy metabolism were measured at ph ysiological temperatures (15 degrees C or 1 degrees C). In the temperate sp ecies, ATP yields from glucose are 3- to 30-fold greater (varying with spec ies) than ATP yields from a monounsaturated fatty acid, while ATP generatio n from glutamate is 2-50 times greater than similar capacities for the lipi d fuel. Like the temperate species, capacity for beta-oxidation of fatty ac ids is limited in the Antarctic species. A positive linear correlation betw een activities of citrate synthase (central pathway of oxidative metabolism ) and hexokinase (glycolysis) adds further support to the hypothesis that g lucose is a preferred metabolic fuel in gill. Our results also demonstrate that fatty acid-binding protein is present in the gill of teleost fishes. I t is likely that this protein plays a more important role facilitating anab olic pathways in lipid metabolism rather than fatty acid oxidation in the g ill of teleost fishes. (C) 1999 Wiley-Liss. Inc.