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Am J Physiol Regul Integr Comp Physiol 274: R1578-R1587, 1998;
0363-6119/98 $5.00
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Vol. 274, Issue 6, R1578-R1587, June 1998

Impact of starvation-refeeding on kinetics and protein expression of trout liver NADPH-production systems

Juan B. Barroso1, Juan Peragón1, Constanza Contreras-Jurado2, Leticia García-Salguero2, Francisco J. Corpas3, Francisco J. Esteban1, María A. Peinado1, Manuel De La Higuera4, and José A. Lupiáñez2

1 Department of Biochemistry and Molecular Biology, Faculty of Experimental Sciences, University of Jaén, E23071 Jaén; 2 Department of Biochemistry and Molecular Biology and 4 Department of Animal Biology and Ecology, Centre of Biological Sciences, University of Granada, E-18001 Granada; and 3 Department of Biochemistry, Cellular and Molecular Biology of Plants, Estación Experimental del Zaidín Consejo Superior de Investigaciones Científicas, E18008 Granada, Spain

Herein we report on the kinetic and protein expression of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase, and malic enzyme (ME) in the liver of the trout (Oncorhynchus mykiss) during a long-term starvation-refeeding cycle. Starvation significantly depressed the activity of these enzymes by almost 60%, without changing the Michaelis constant. The time response to this nutritional stimulus increased with fish weight. The sharp decline in G6PDH and ME activities was due to a specific protein-repression phenomenon, as demonstrated by molecular and immunohistochemical analyses. Also, the dimeric banding pattern of liver G6PDH shifted from the fully reduced and partially oxidized forms, predominant in control, to a fully oxidized form, more sensitive to proteolytic inactivation. Refeeding caused opposite effects in both protein concentration and enzyme activities of about twice the control values in the first stages, later reaching the normal enzyme activity levels. Additionally, the partially oxidized form of G6PDH increased. The kinetics of these enzymes were examined in relation to the various metabolic roles of NADPH. These results clearly indicate that trout liver undergoes protein repression-induction processes under these two contrasting nutritional conditions.

rainbow trout; low-fat and high-carbohydrate diet; glucose-6-phosphate dehydrogenase; 6-phosphogluconate dehydrogenase; malic enzyme; dimeric banding pattern; immunohistochemistry


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