Fig. 1. Photomicrographs and primary data sets for protein synthesis and respiration rate measurements of 13-day-old fed larvae of Lytechinus pictus. (A) Photomicrograph of 13-day-old unfed and (B) fed larvae. Scale bars, 200 µm. (C) Linear increase of [¹⁴C]alanine incorporation into the protein pool (TCA-insoluble fraction) of 13-day-old fed larvae of L. pictus: y=41.4(±2.71)x–68.4 (r²=0.98; P<0.001). Rates of [¹⁴C]alanineincorporation were converted to absolute rates of protein synthesis (ng protein individual^-1 h^-1) using the change in the specific activity of [¹⁴C]alanine in the precursor free amino acid pool (Fig. 1E), the mole-percent of alanine in protein (7.8%; Table 1) and the mole-percent corrected molecular mass for amino acids in protein (129.4 g mole^-1; Table 1). (D) Chromatogram of extracted free amino acid pool from 13-day-old larvae of L. pictus separated using high performance liquid chromotagraphy (HPLC). D, aspartate; E, glutamate; N, asparagine; S, serine; H, histidine; G, glycine; R, arginine. Alanine was the [¹⁴C]amino acid tracer used to determine rates of protein synthesis. (E) Specific activity of [¹⁴C]alanine in the free amino acid pool during protein synthesis experiments with 13-day-old larvae of L. pictus. Specific activity was measured at the specified sampling intervals by quantifying the moles of total alanine with HPLC (as in Fig. 1D). [¹⁴C]alanine was measured by liquid scintillation counting of the radioactivity associated with the alanine peak fraction. Increase of specific activity was described by the linear equation: y=39.2(±3.85)x+279.9 (r²=0.96; P<0.001 for ANOVA of regression slope). (F) Respiration rate of 13-day-old fed larvae of L. pictus. Each data point represents a different respiration chamber. Respiration rate was calculated by determining the slope of total oxygen consumption in each respiration chamber for the known number of larvae in that chamber: y=109.5(±8.4)x+1254 (r²=0.97; P<0.0001), where the slope of 109.5 has units of pmol O₂ larva^-1 h^-1.