THE RELATIONSHIP BETWEEN SPECIFIC DYNAMIC ACTION (SDA) AND PROTEIN-SYNTHESIS RATES IN THE CHANNEL CATFISH

The purpose of the study was to investigate the relationship between specific dynamic action (SDA) and the rate of protein synthesis following a simulated meal consisting of an essential amino acid infusion. After such an infusion, the O2 consumption rates of catfish approximately doubled, and the rate of protein synthesis in white muscle rose from 1.3 to 2.86 mg g-1 d-1. After pretreatment with the protein synthesis inhibitor cycloheximide, there was no significant SDA (defined as the increase in oxygen consumption) and the rate of protein synthesis fell to 0.34 mg g-1 d-1. There was good agreement between the magnitude of the SDA observed, the magnitude of the increase in protein synthesis, and theoretical calculations of the expected metabolic costs of protein synthesis based on oxygen equivalents for ATP production and ATP requirements for protein formation. The results support the idea that SDA may be directly attributable to the cost of protein synthesis, and therefore to the metabolic cost of growth.