ULTRASTRUCTURAL BASES FOR METABOLICALLY LINKED MECHANICAL ACTIVITY IN MITOCHONDRIA

Isolated mitochondria are capable of undergoing dramatic reversible ultrastructural transformations between a condensed and an orthodox conformation. These two conformations are the extremes in ultrastructural organization between which structually and functionally intact mitochondria transform during reversible respiratory cycles. It has been found that electron transport is required for the condensed-to-orthodox ultrastructural transformation which occurs in mitochondria under State IV conditions, i.e., under conditions in which exogenous substrate is present and ADP is deficient. Inhibition of State IV electron transport at the cyanide-, antimycin A-, or Amytal-sensitive sites in the respiratory chain results in inhibition of this transformation. Resumption of electron transport in initially inhibited mitochondrial systems, initiated by channeling electrons through pathways which bypass the inhibited sites, results in resumption of the ultrastructural transformation. The condensed-to-orthodox transformation is DNP insensitive and, therefore, does not require participation of the coupling enzymes of the energy-transfer pathway. It is concluded that this ultrastructural transformation is manifest by the conversion of the chemical energy of electron transport directly into mechanical work. The reversed ultrastructural transformation, i.e., orthodox-to-condensed, which occurs during ADP-activated State III electron transport, is inhibited by DNP and parallels suppression of acceptor control and oxidative phosphorylation. Mechanochemical ultrastructural transformation as a basis for energy transfer in mitochondria is considered with respect to the results presented.

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Carbon-Heteroatom Cross-Coupling via an Electronically Excited Nickel (II) Complex

10.26434/chemrxiv.9736049.v1 ◽

2019 ◽

Author(s):

Randolph Escobar ◽

Jeffrey Johannes

Keyword(s):

Energy Transfer ◽

Functional Groups ◽

Cross Coupling ◽

Reductive Elimination ◽

Aryl Halides ◽

Coupling Reactions ◽

General Methodology ◽

Cross Coupling Reactions ◽

Electronically Excited ◽

Energy Transfer Pathway

<div>While carbon-heteroatom cross coupling reactions have been extensively studied, many methods are specific and</div><div>limited to a set of substrates or functional groups. Reported here is a method that allows for C-O, C-N and C-S cross coupling reactions under one general methodology. We propose that an energy transfer pathway, in which an iridium photosensitizer produces an excited nickel (II) complex, is responsible for the key reductive elimination step that couples aryl halides to 1° and 2° alcohols, anilines, thiophenols, carbamates and sulfonamides.</div>

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The mitochondrial consequences of uncoupling intact cells depend on the nature of the exogenous substrate

Biochemical Journal ◽

10.1042/bj3550231 ◽

2001 ◽

Vol 355 (1) ◽

pp. 231-235 ◽

Cited By ~ 6

Author(s):

Brigitte SIBILLE ◽

Céline FILIPPI ◽

Marie-Astrid PIQUET ◽

Pascale LECLERCQ ◽

Eric FONTAINE ◽

...

Keyword(s):

Oxidation Rate ◽

Marked Decrease ◽

Electrical Potential ◽

Atp Synthesis ◽

Intact Cells ◽

Isolated Mitochondria ◽

Exogenous Substrate ◽

High Oxidation ◽

Transmembrane Electrical Potential ◽

Sustained Increase

In isolated mitochondria the consequences of oxidative phosphorylation uncoupling are well defined, whereas in intact cells various effects have been described. Uncoupling liver cells with 2,4-dinitrophenol (DNP) in the presence of dihydroxyacetone (DHA) and ethanol results in a marked decrease in mitochondrial transmembrane electrical potential (∆ψ), ATP/ADP ratios and gluconeogenesis (as an ATP-utilizing process), whereas the increased oxidation rate is limited and transient. Conversely, when DHA is associated with octanoate or proline, DNP addition results in a very large and sustained increase in oxidation rate, whereas the decreases in ∆ψ, ATP/ADP ratios and gluconeogenesis are significantly less when compared with DHA and ethanol. Hence significant energy wastage (high oxidation rate) by uncoupling is achieved only with substrates that are directly oxidized in the mitochondrial matrix. Conversely in the presence of substrates that are first oxidized in the cytosol, uncoupling results in a profound decrease in mitochondrial ∆ψ and ATP synthesis, whereas energy wastage is very limited.

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A Single Amino Acid Alteration in PGR5 Confers Resistance to Antimycin A in Cyclic Electron Transport around PSI

Plant and Cell Physiology ◽

10.1093/pcp/pct098 ◽

2013 ◽

Vol 54 (9) ◽

pp. 1525-1534 ◽

Cited By ~ 32

Author(s):

Kazuhiko Sugimoto ◽

Yuki Okegawa ◽

Akihiko Tohri ◽

Terri A. Long ◽

Sarah F. Covert ◽

...

Keyword(s):

Amino Acid ◽

Electron Transport ◽

Single Amino Acid ◽

Antimycin A ◽

Cyclic Electron Transport ◽

Acid Alteration ◽

Amino Acid Alteration

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Green Bacteria – Energy Transfer and Electron Transport

Reference Module in Life Sciences ◽

10.1016/b978-0-12-819460-7.00031-1 ◽

2020 ◽

Author(s):

Hirozo Oh-oka ◽

Jiro Harada ◽

Chihiro. Azai

Keyword(s):

Energy Transfer ◽

Electron Transport ◽

Green Bacteria

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Oil Sands Derived Naphthenic Acids Are Oxidative Uncouplers and Impair Electron Transport in Isolated Mitochondria

Environmental Science & Technology ◽

10.1021/acs.est.8b02638 ◽

2018 ◽

Vol 52 (18) ◽

pp. 10803-10811 ◽

Cited By ~ 5

Author(s):

Kate I. Rundle ◽

Mahmoud S. Sharaf ◽

Don Stevens ◽

Collins Kamunde ◽

Michael R. van den Heuvel

Keyword(s):

Electron Transport ◽

Oil Sands ◽

Naphthenic Acids ◽

Isolated Mitochondria

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Phycobilisomes Harbor FNRL in Cyanobacteria

mBio ◽

10.1128/mbio.00669-19 ◽

2019 ◽

Vol 10 (2) ◽

Cited By ~ 9

Author(s):

Haijun Liu ◽

Daniel A. Weisz ◽

Mengru M. Zhang ◽

Ming Cheng ◽

Bojie Zhang ◽

...

Keyword(s):

Mass Spectrometry ◽

Energy Transfer ◽

Electron Transport ◽

Carbon Fixation ◽

Close Association ◽

Reaction Centers ◽

Light Energy ◽

Fine Tuning ◽

Cyclic Electron Transport ◽

Cross Link

ABSTRACT Cyanobacterial phycobilisomes (PBSs) are photosynthetic antenna complexes that harvest light energy and supply it to two reaction centers (RCs) where photochemistry starts. PBSs can be classified into two types, depending on the presence of allophycocyanin (APC): CpcG-PBS and CpcL-PBS. Because the accurate protein composition of CpcL-PBS remains unclear, we describe here its isolation and characterization from the cyanobacterium Synechocystis sp. strain 6803. We found that ferredoxin-NADP+ oxidoreductase (or FNRL), an enzyme involved in both cyclic electron transport and the terminal step of the electron transport chain in oxygenic photosynthesis, is tightly associated with CpcL-PBS as well as with CpcG-PBS. Room temperature and low-temperature fluorescence analyses show a red-shifted emission at 669 nm in CpcL-PBS as a terminal energy emitter without APC. SDS-PAGE and quantitative mass spectrometry reveal an increased content of FNRL and CpcC2, a rod linker protein, in CpcL-PBS compared to that of CpcG-PBS rods, indicative of an elongated CpcL-PBS rod length and its potential functional differences from CpcG-PBS. Furthermore, we combined isotope-encoded cross-linking mass spectrometry with computational protein structure predictions and structural modeling to produce an FNRL-PBS binding model that is supported by two cross-links between K69 of FNRL and the N terminus of CpcB, one component in PBS, in both CpcG-PBS and CpcL-PBS (cross-link 1), and between the N termini of FNRL and CpcB (cross-link 2). Our data provide a novel functional assembly form of phycobiliproteins and a molecular-level description of the close association of FNRL with phycocyanin in both CpcG-PBS and CpcL-PBS. IMPORTANCE Cyanobacterial light-harvesting complex PBSs are essential for photochemistry in light reactions and for balancing energy flow to carbon fixation in the form of ATP and NADPH. We isolated a new type of PBS without an allophycocyanin core (i.e., CpcL-PBS). CpcL-PBS contains both a spectral red-shifted chromophore, enabling efficient energy transfer to chlorophyll molecules in the reaction centers, and an increased FNRL content with various rod lengths. Identification of a close association of FNRL with both CpcG-PBS and CpcL-PBS brings new insight to its regulatory role for fine-tuning light energy transfer and carbon fixation through both noncyclic and cyclic electron transport.

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