To study the influence of genetics and feeding strategy, we measured growth and mRNA expression of protein degradation markers in growth‐selected and control rainbow trout that were either fed to satiation or limit‐fed. Fish were limit fed to 90–95% of the feed required to reach maximal growth. Length and weight of 1600 trout were measured every six weeks for 24 weeks. After 24 weeks of dietary treatment there was an interaction (p<0.05) between genetics and feeding strategy for both length and weight. The least squares means ± the standard error of the means for weight of satiation/control, limit‐fed/control, satiation/selected and limit‐fed/selected fish were 371 ± 6, 350 ± 4, 544 ± 24, and 426 ± 16 grams and for length 299 ± 2, 291 ± 2, 347 ± 2 and 330 ± 2 mm, respectively. mRNA expression of 4 components of the ubiquitin/proteasome machinery were decreased (p<0.05) by an average of 17% in muscle of the growth‐selected fish consistent with a reduced capacity to degrade protein. No effect of feeding strategy was seen for mRNA expression nor was an interaction detected. No differences in IGF‐1 concentrations were detected due to feeding strategy or genetics. This suggests decreased degradation of protein through proteasomes and caspases could be the cause for increased weight and length of the growth‐selected trout. Support: Aquaculture Product and Marketing Development Project.

The objective was to investigate diet‐induced alterations in hepatic lysine catabolism via the saccharopine‐dependent pathway in pigs. This pathway depends on the bifunctional α‐aminoadipate δ‐semialdehyde synthase (AASS), which contains both lysine α‐ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH) activities. In liver, LKR and SDH are restricted to the mitochondrial matrix and lysine is presumably transported through the inner membrane by one or both isoforms of ornithine transporters (ORC‐1/2). Weanling pigs (7 litters, 5/litter) were fed either a control (C, 18% CP, 0.95% lys), high protein (HP, 23% CP, 0.95% lys), low protein (LP, 13% CP, 0.95% lys), high lysine (HL, 18% CP, 1.25% lys) or low lysine (LL, 18% CP, 0.65% lys) diet for 10 days. No differences in weight gain or feed intake were detected. LKR (P<0.05) and SDH (P<0.05) activities and AASS protein abundance (P<0.01) were reduced 30, 35 and 52% respectively, in pigs consuming the LL diet relative to C. ORC‐1 mRNA expression increased (170%, P<0.05) with consumption of the HL diet and decreased (50%) with consumption of the LL diet; ORC‐2 mRNA expression was not affected by dietary treatment, although it tended to be higher (88%) in the HL and lower (76%) in the LL fed pigs relative to C. These data are consistent with ORC1/2 delivering lysine to the matrix and marks them as potential regulators of lysine catabolism (Support; HATCH WVA 470).

In typical turkey production diets, lysine is frequently the second limiting amino acid. Understanding its catabolism could provide opportunities to increase the efficiency of lysine use for protein synthesis. We hypothesize that indices of lysine catabolism in turkey liver vary throughout the production cycle. Two commercial strains of turkey, Hybrid and Nicolas, were analyzed 8 times over a period of 17 weeks (n=8 birds/sampling time/strain) for lysine α‐ketoglutarate (LKR) and saccharopine dehydrogenase (SDH) activity and mRNA abundance, in vitro lysine oxidation (LOX) and amino acid oxidase (AAOX) activity. We found differences in LKR mRNA (P<0.01), SDH activity (P<0.05) and LOX (P<0.0001) and a trend for differences in LKR activity (P=0.09), SDH mRNA (P=0.07) and AAOX activity (P=0.06) throughout the production cycle. No consistent strain differences were detected for any variable. Interestingly, the average LKR and SDH activities across strains and weeks was 230 and 400 nmol per minute per gram of liver, respectively, as opposed to the average AAOX activity and LOX was 1.25 and 13.6 nmol per minute per gram liver, respectively. These data indicate that the saccharopine‐dependent pathway is the predominant pathway of lysine degradation in turkey liver and that indices of hepatic lysine catabolism vary throughout the production cycle. (Support; HATCH WVA 470, Virginia Poultry Growers Cooperative)

The primary pathway of lysine degradation in pigs presumably depends on the bifunctional protein α‐aminoadipate δ‐semialdehyde synthase (AASS) which contains lysine α‐ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH) activities. In liver, AASS is restricted to the mitochondrial matrix and lysine is transported, presumably, by one or both mitochondrial ornithine transporters (MOT1/MOT2). Lysyl oxidase (LylOx) may represent a minor pathway of lysine oxidation. We assessed LKR, SDH and LylOx activities, lysine oxidation, mRNA abundance of LKR and MOT1/2 and AASS protein abundance (via SDH antibody) in liver, heart, kidney medulla and cortex, enterocytes, triceps and longissimus. In growing pigs (n=5), tissues oxidized lysine at varying rates. LKR activity was highest in liver (P<0.05). LKR mRNA abundance in liver was 6 to 130‐fold greater than other tissues (P<0.05). No differences in SDH activity across tissues were detected. No AASS protein could be detected in muscle. LylOx activity was highest in muscle. MOT1 and 2 were detected in every tissue, although no differences were detected as a function of tissue; interestingly there was a significant correlation between LKR activity and MOT1 mRNA abundance (P<0.05, R 2 = 0.48). These data indicate that extra‐hepatic tissues contribute to lysine oxidation as do enzymes other than LKR. (Support; HATCH WVA 470)