Regulatory features of protein synthesis in isolated mitochondria from Artemia embryos

Optimal conditions were developed for measuring rates of protein synthesis in isolated mitochondria from encysted embryos of Artemia franciscana to 1) identify the required chemical constituents, 2) assess the influence of extramitochondrial pH on protein synthesis, and 3) investigate potential mechanisms coordinating nuclear and mitochondrial gene expression. Isolation procedures resulted in intact, highly coupled mitochondria [respiratory control ratio = 6.48 +/- 0.43 (SE), n = 21]. Requirements for maximal rates of protein synthesis, measured as incorporation of [3H]leucine (60 microM), included an oxidizable carbon source (10 mM succinate), adenine nucleotides (1.5 mM ADP), phosphate (10 mM), K+ (125 mM), Mg2+ (10 mM), amino acids (0.3 mM of each), sucrose or trehalose (500 mM), EGTA (1 mM), and bovine serum albumin (1 mg/ml). Rates were linear for 60 min at 25 degrees C (r = 0.99). Fluorography of translated products revealed 13 peptides. Previous research has shown that anoxia-induced acidification of intracellular pH (pHi) results in suppression of protein biosynthesis, as judged by cytochrome-c oxidase synthesis. In the present study, mitochondrial protein synthesis was acutely sensitive to external pH, with 80% inhibition observed by lowering pH from 7.5 to 6.8. Thus acidification of pHi may serve as one intracellular signal contributing to a coordinated suppression of both cytoplasmic and mitochondrial protein synthesis during transitions from active to anoxia-induced quiescent states.