Extension of enzyme half-life during quiescence in Artemia embryos
Encysted gastrulae of Artemia franciscana are known to enter a reversible state of quiescence in which biosynthetic and catabolic pathways are markedly suppressed. Given that these embryos can survive months of anoxia, we investigated their ability to extend the half-life of cytochrome-c oxidase (COX), a key metabolic enzyme, during anoxia. We calculate that the half- life of COX is extended to 101 days under anoxia, an estimated 77-fold increase compared with aerobic values. During conditions of aerobic acidosis, the half-life of COX was extended sevenfold to a value of 9.7 days. We propose that the extended lifetimes of COX in both cases may be due to suppressed mitochondrial proteolysis under depressed pH. The shorter enzyme half-life observed under the latter condition may be due to the availability of ATP for degradative processes during aerobic acidosis. We also suggest that the presence of oxygen in aerobic acidosis may lead to increased rates of protein damage due to autooxidation.