PACE, D.A.*; MAXSON, R.E.; MANAHAN, D.T.; Univ. Southern California, Los Angeles; Univ. Southern California; Univ. Southern California: High rates of protein synthesis and rapid ribosomal transit times at low energy cost in Antarctic echinoderm embryos

Cold oceanic environments represent a major part of the biosphere. Most animals living in these �extreme� environments have life-history stages with larval development. Little is known about physiological processes that might be unique to animal development in these conditions. We report that costs of protein synthesis in embryos and larvae developing in Antarctic waters are ca. an order of magnitude lower than values published for protein synthesis in most other animals. In the Antarctic sea urchin Sterechinus neumayeri the cost of synthesis, measured using protein synthesis inhibitors, was 0.83 � 0.21 Joules (mg protein synthesized)^-1. In the Antarctic seastar Odontaster validus the cost of synthesis, based on the relationship of protein synthesis and oxygen consumption, was also low at 1.93 � 0.44 Joules (mg protein synthesized)^-1. The biochemical bases for this high-efficiency metabolism were studied at the subcellular level in embryos of S. neumayeri by measuring the rates of peptide elongation and the number of ribosomes engaged in protein synthesis. At -1.5�C ribosomal activity was high, with an average transit time on mRNA transcripts of 25.9 � 2.02 minutes. This transit time equates to a peptide elongation rate of 0.39 codons second^-1 and is comparable to rates measured in temperate species of sea urchins at much higher temperatures (15-17�C). Rates of protein synthesis calculated from cell-free in vitro measurements on Antarctic sea urchins confirm high rates of protein synthesis measured on whole embryos of the same species in vivo at -1.5�C. These rapid ribosomal transit times and low protein synthesis costs demonstrate unique physiological capabilities in these Antarctic organisms.