Regulation of the kinetic behavior of serine dehydratase and tyrosine aminotransferase during the development of rainbow trout (Oncorhynchus mykiss)

Serine dehydratase (SerDH) and tyrosine aminotransferase (TyrAT) are regulatory enzymes of serine and tyrosine catabolism in trout. Here, we have studied the kinetic behavior of SerDH and TyrAT in liver and white muscle of rainbow trout (Oncorhynchus mykiss) at different stages of development (fingerling: 14-week-old trout; juvenile: 24-, 28-, 40-week-old trout; adult: 96-week-old trout). SerDH and TyrAT showed hyperbolic kinetics in all developmental stages. A significant and progressive decrease in the specific activity, maximum velocity and catalytic efficiency of hepatic SerDH and hepatic and white-muscle TyrAT was observed during development. Nevertheless, the specific TyrAT activity per cell unit was similar in the fingerling and adult stages. No significant changes were found in the Michaelis constant of the different groups of age. This behavior is consistent with the existence of a regulation of the number of enzyme molecules. Total TyrAT activity was of similar magnitude in liver and in white muscle in the fingerling and adult stages. These results show that, in trout, SerDH and TyrAT are two inducible enzymes regulated by the development that showed their highest levels during the first stages, in which the highest whole-body growth rate was found. These results imply high serine and tyrosine requirements in fingerling and juvenile stages that should be considered in the formulation of trout diet for these stages.