Sanchez-Muros MJ ; Garcia-Rejon L ; Lupianez JA ; de la Higuera M ;

Aquaculture Nutrition vol. 1 (4)   pp. 213-220, 1995

Dep. de Biol. Anim. y Ecologia, Facultad de Cienc., Univ. de Granada, Avenida Fuentanueva s/n. 18001 Granada, Spain

The adaptive response of the kinetics of glucose 6-phosphate dehydrogenase (G6PDH) was studied in trout liver and kidney after feeding (control or high-protein/non-carbohydrate diet) or starving for 30 days, as well as influences on growth and other nutritive parameters. Typical Michaelis-Menten kinetics were found for the hepatic catalysis of G6PDH under all conditions studied, without evidence of sigmoidicity. The administration of a high-protein/non-carbohydrate diet (61.0% protein, 7.9% lipids) produced no significant changes in specific activity or other kinetic parameters of the liver enzyme. This nutritional situation caused a significant daily increase in relative growth (20%) and feed efficiency (13.5%), as well as a 13% decrease in the protein-conversion efficiency, with respect to the control diet (46% protein, 8% lipids, 22% carbohydrates). On the other hand, long-term starvation (30 days), as a lipolytic condition, significantly decreased the activity and catalytic efficiency of hepatic G6PDH, by almost 45%, without significant changes in the K sub(m) and activity-ratio values. These changes agree with a fall in the intracellular concentration of the enzyme as a consequence of a protein-repression process. The activity of the renal G6PDH was less than in the liver of control fish, and no variation in kinetics was found under the high-protein diet or starvation. This behaviour clearly demonstrates that the kidney pentose-phosphate pathway showed no adaptive response in relation to synthesis of fatty acids and other lipids

Nutritional requirements ;  Liver ;  Kidneys ;  Animal metabolism ;  Fish physiology ;  Diets ;  Starvation ;  Enzymatic activity ;  Oncorhynchus mykiss ;