February 15-18, 2009 Washington State Convention Center Seattle ...

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EFFECT OF AMINO ACID DEFICIENCY AND FISH STRAIN ON PROTEIN DEGRADATION
SYSTEMS IN RAINBOW TROUT
T. Gibson Gaylord, Kenneth E. Overturf and Frederic T. Barrows
USDA-ARS Small Grains and Potato Germplasm Research Unit
Hagerman Fish Culture Experiment Station
3059F National Fish Hatchery Rd.
Hagerman, ID 83332 USA
Growth is known to be impaired due to amino acid deficiencies and is variable in different strains of trout. Alterations in degradation
pathways due to amino acid imbalances as well as variability between strains of trout have not been widely examined. In
order to assess changes in protein degradation systems, specifically the 20S proteosome and calpain systems, two experiments
were devised and carried out. The first experiment was designed to determine differences in protein degradation pathways
when diets were deficient in either methionine (13 vs. 19 g TSAA/kg diet) or lysine (12 vs. 29 g lysine/kg diet). The second
experiment investigated genetic differences between two strains of rainbow trout (R9 vs. House Creek) in the 20S proteosome
and calpain degradation systems when diets were either deficient or adequate in methionine.
In experiment 1, growth, feed consumption, feed conversion ratios, whole body crude protein and protein retention efficiencies
were negatively affected by deficiency of either amino acid. Feed consumption, whole body crude protein and protein retention
efficiency, were affected by both amino acid type as well as deficiency. Interactive effects of amino acid type and deficiency
on protein retention efficiency indicate that lysine deficiency reduced protein retention more than methionine deficiency. Feeding
diets with inadequate amino acid content increased the rates of both the calpain and 20S proteosome degradation systems.
Higher 20S proteosome activity was observed for the fish fed the lysine deficient diet than the fish fed the methionine deficient
diet.
In experiment 2, diet and strain both had significant effects on all growth and condition indices. Significant interactive effects
also were observed for growth (% gain and SGR), whole body crude protein, and protein retention efficiencies. Feeding methionine
deficient diets restricted growth potential for the House Creek strain to a greater extent than feeding the same diets to
the R9 strain.
The calpain and 20S proteosome degradation activities were elevated in fish consuming a methionine deficient diet compared
to the sufficient diet. No strain effects were observed on degradation activities of the two systems. However, there was a strain
effect on fish performance criteria.
In conclusion, it appears that there are differences in the regulation of the calpain and 20S proteosome protein degradation systems
based on which amino acid is limiting (lys vs. met, in experiment 1). While no strain effects were observed for the protein
degradation systems there appears to be differential utilization of amino acids for meeting the genetic potential of a trout strain
due to the observation that the House Creek strain had greater PRE when the diet was not limited by methionine.