PACE, DA; MANAHAN, DT: Differential protein accretion rates and energetic efficiency of protein synthesis during sea urchin development.

The continual synthesis and degradation of protein is critical for growth and development in early life stages. The goal of the present study was to determine the energetic cost of protein synthesis in embryos and larvae of the white sea urchin, Lytechinus pictus, and to assess whether there is significant variation in the cost of synthesis due to: 1) differences in rates of protein accretion and 2) techniques employed for determining the cost of protein synthesis. The cost of protein synthesis was determined for fed and unfed larvae. The treatments resulted in large differences in protein growth rates (fed and unfed larvae at 19 and -0.24 ng protein d^-1, respectively). There were no significant differences, however, in the costs of protein synthesis: fed and unfed ( ± SEM) = 5.90 ± 0.97 and 6.34 ± 2.95 joules (mg protein synthesized)^-1, respectively. Two different methods of determining the cost of protein synthesis were investigated to determine if there was general agreement between these commonly-used methods. Firstly, cost was measured based on the relationship of respiration and protein synthetic rates (indirect, ‘correlative cost’ analysis); secondly, cost of synthesis was measured by comparing respiration rates of larvae in the presence and absence of a protein synthesis inhibitor (direct, ‘inhibitor cost’ analysis). The costs of protein synthesis were similar when measured with each method (correlative and inhibitor costs = 6.34 ± 0.36 and 9.8 ± 2.0 joules (mg protein synthesized)^-1. Our results show that for developmental stages of this species of sea urchin, the cost of protein synthesis is independent of the rate of growth.