Diguanosine nucleotide metabolism and the survival of artemia embryos during years of continuous anoxia

Abstract

Encysted embryos of the primitive crustacean, Artemia franciscana, are remarkably resistant to a variety of harsh environmental conditions, including continuous anoxia for periods of years at physiological temperatures and water contents. Previous study produced no evidence of an ongoing anoxic metabolism, suggesting that these embryos remained viable in spite of the lack of detectable free energy flow and biosynthesis. That seeming violation of a major axiom of cell biology and biochemistry prompted us to re-examine the nucleotide pool of encysted embryos during prolonged anoxia. We found that the nucleotide Gp4G, present initially in very large amounts, decreased slowly as anoxia continued over the 5.6-year period examined. Studies on other nucleotides and associated enzymes, including results from previous papers, provide a plausible metabolic pathway leading to the provision of ATP and GTP to meet the needs of endergonic processes in anoxic embryos. Exactly what those processes are is not obvious. One possibility involves the extensive anoxia-induced nuclear translocation of the stress protein, molecular chaperone p26, whose large molecular mass (≈ 500 kDa) most likely requires a supply of free energy to cross the nuclear envelope. Support for this possibility comes from our finding here that p26 is also a GTPase.