Comparative study on the kinetic behaviour of carnitine palmitoyltransferase I between Javelin gobySynechogobius hasta(carnivorous) and grass carpCtenopharyngodon idella(herbirovous)

Abstract

Up to date, the carnitine palmitoyltransferase (CPT) system in fish nutrition receives little attention. The present study compared CPT I kinetic behaviour of Synechogobius hasta (carnivorous) and Ctenopharyngodon idella (herbivorous). The optimal conditions (temperature, incubation time, mitochondrial protein concentration and pH) for maximum CPT I activity showed no significant difference between S. hasta and C. idella. CPT I activities in S. hasta were significantly higher than those in C. idella. Affinity constants (Km) for carnitine in liver, heart, white muscle and spleen of S. hasta were significantly higher than those in C. idella. Km for palmitoyl-CoA in liver and heart of S. hasta were significantly higher than those in C. idella. Vmax for carnitine and palmitoyl-CoA in S. hasta tended to be higher than those in C. idella. Catalytic efficiencies (Vmax/Km) for carnitine in liver, white muscle and spleen of C. idella were significantly higher than those in S. hasta. Vmax/Km values for palmitoyl-CoA in liver and heart of C. idella were higher than those in S. hasta. Our study demonstrated that the lower catalytic efficiency for carnitine in liver of S. hasta indicated that the fish showed a low capacity for energy generation through β-oxidation of long-chain fatty acids, which easily caused fatty liver syndrome. This is the first study in which, by using carnitine and palmitoyl-CoA as the substrates, the complete kinetic characterization of CPT I in fish has been described, which increases our knowledge about lipid metabolism and its critical role in lipid utilization in fish.