LONG-TERM NUTRITIONAL EFFECTS ON THE PRIMARY LIVER AND KIDNEY METABOLISM IN RAINBOW-TROUT - ADAPTIVE RESPONSE TO STARVATION AND A HIGH-PROTEIN, CARBOHYDRATE-FREE DIET ON GLUTAMATE-DEHYDROGENASE AND ALANINE AMINOTRANSFERASE KINETICS

In fish, metabolic changes and qualitative responses during different nutritional situations are highly controversial in the scientific lite rature, and for this reason the objective of this work has been to pro be deeper into the adaptive behaviour of two important amino acid-meta bolising enzymes, glutamate dehydrogenase (GDH) and alanine aminotrans ferase (AAT) of liver and kidney in trout. In the present study, we ex amined the long-term effects of endogenous or exogenous proteins-gener ated, respectively, by a prolonged starvation or by feeding a high-pro tein diet-on the kinetics of liver and kidney GDH and AAT. Feeding on a high-protein diet significantly increased the liver (100%) and kidne y (49%) GDH V-max and catalytic efficiency; the same kinetic parameter s of AAT increased by 65% only in the liver enzyme, without changing t he K-m and activity ratio values. Starvation registered a significant increase of both enzymes, V-max and catalytic efficiency in the liver, but activity was unaltered in the kidney. In addition, no significant changes were found in the K-m or activity ratio. All enzyme kinetics showed a Michaelian behaviour without any evidence of sigmoidicity. Th e experimental results show strong adaptive responses in the kinetic b ehaviour of the enzymes of both tissues. With the exception of renal A AT, the remainder of the enzymes presented a mal-ked influence in thei r kinetic parameters by an excess of protein. The results are discusse d in terms of the possible adaptive role of enzyme kinetics to amino a cid availability. (C) 1998 Elsevier Science Ltd. All rights reserved.