Serine dehydratase and tyrosine aminotransferase activities increased by long‐term starvation and recovery by refeeding in rainbow trout (Oncorhynchus mykiss)

Abstract

Here, we study a cycle of long-term starvation followed by refeeding in relation to the kinetics of serine dehydratase (SerDH) and tyrosine aminotransferase (TyrAT) in rainbow trout (Oncorhynchus mykiss). We determine SerDH- and TyrAT- specific activity at different substrate concentrations in liver and white muscle of juvenile trout starved for 70 days and then refed for 6 hr, 32 hr, 4 days, and 9 days. SerDH showed a hyperbolic kinetic with a K(m) for L-serine of 77.07+/-8.78 mM in the liver of control trout. After 70 days of starvation, the SerDH activity at saturate substrate concentration rose 100% over control. No significant changes were found in the K(m) values of the enzyme. After refeeding, the SerDH activity declined to control values. TyrAT also showed a hyperbolic kinetic with a K(m) for L-tyrosine of 1.86+/-0.12 and 2.55+/-0.57 mM in liver and white muscle, respectively. In starved trout, TyrAT activity in liver and white muscle was about 64 and 267%, respectively, higher than control. After 9 days of refeeding, the control values recovered, although, at 6 hr of refeeding, hepatic TyrAT activity was higher than that for starvation. This work shows that SerDH and TyrAT are present in rainbow trout and that the two enzymes have regulatory functions in the catabolism of their respective amino acids in this species.