Hand 2013 Abstract MiP2013

Hand SC, Patil Y (2013) Defense against ATP depletion during the energy-limited state of diapause. Mitochondr Physiol Network 18.08.

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MiP2013, Book of Abstracts Open Access

Hand SC, Patil Y (2013)

Event: MiPNet18.08_MiP2013

Gastrula-stage embryos of Artemia franciscana (brine shrimp) undergo dramatic respiratory depression and developmental arrest upon release from the adult female as they enter a state of hypometabolism termed diapause [1]. Metabolism as measured by respiration rate declines by over 99% during entry into diapause across a 26-day time course [2]. The primary basis for the inhibition is a restriction of oxidative substrate to the mitochondrion that involves an orchestrated interplay at multiple enzymatic sites including trehalase, hexokinase, pyruvate kinase and pyruvate dehydrogenase [2].

While a substantial decrease in embryo ATP occurs during diapause, a significant amount of ATP remains [e.g., ATP:ADP ratio = 1.306 ± 0.036 (mean ± SE, N = 10)]. This observation is noteworthy when one considers that proton conductances of mitochondria isolated from diapause and post-diapause embryos are identical when compared as a function of the driving force (ΔΨ) [2]. Thus proton leak apparently is not downregulated during diapause, and as a consequence, mitochondrial ΔΨ is likely severely compromised because respiration of intact embryos is depressed far below that required to compensate for leak. Under such conditions, one would predict that the F1Fo-ATP synthase could reverse and fully deplete cellular ATP. Because ATP is not depleted, we predict that the F1Fo-ATP synthase is blocked during diapause by the F1-ATPase inhibitor protein IF1. This 9.6 kDa protein binds to the ATP synthase at the F1 catalytic domain and inhibits the hydrolytic activity of the enzyme under conditions where ΔΨ is low [3]. Further, acidic pH is known to promote the formation of the active dimeric state of IF1 and a stable complex with the enzyme [3]. It is likely that intracellular pH of A. franciscana embryos may decline during diapause as the metabolic depression phase progresses.

IF1 could potentially explain the conservation of adenylates in diapause. Affinity purification [4] and characterization of the ATP synthase from A. franciscana and its interaction with IF1 is underway.

• Keywords: Diapause, Inhibitor protein IF1

• O2k-Network Lab: US_LA Baton Rouge_Hand SC

Labels: MiParea: Respiration, Comparative MiP;environmental MiP, Developmental biology 

Organism: Artemia, Crustaceans 

Preparation: Intact organism, Homogenate, Isolated mitochondria, Enzyme  Enzyme: Complex V;ATP synthase  Regulation: ADP, ATP, mt-Membrane potential, pH  Coupling state: LEAK, OXPHOS, ET  Pathway: N, S  HRR: Oxygraph-2k 

MiP2013, S03 

Affiliations and author contributions

1 - Division of Cellular, Developmental, and Integrative Biology, Dept of Biol Sci, Louisiana State University, Baton Rouge, USA;

2 - Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge, USA.

Email: [email protected]

Supported by NSF grant IOS-0920254 and NIH grant 2 RO1 DK046270-14A1

References

1. Hand SC, Menze MA, Borcar A, Patil Y, Covi JA, Reynolds JA, Toner M (2011) Metabolic restructuring during energy-limited states: Insights from Artemia franciscana embryos and other animals. J Insect Physiol 57: 584-594.
2. Patil Y, Marden B, Brand MD, Hand SC (2013) Metabolic downregulation and inhibition of carbohydrate catabolism during diapause in embryos of Artemia franciscana. Physiol Biochem Zool 86: 106-118.
3. Bason JV, Runswick MJ, Fearnley IM, Walker JE (2011) Binding of the inhibitor protein IF1 to bovine F1-ATPase. J Mol Biol 406: 443-453.
4. Runswick MJ, Bason JV, Montgomery MG, Robinson GC, Fearnley IM, Walker JE (2013) The affinity purification and characterization of ATP synthase complexes from mitochondria. Open Biol 3: 120160.