scholarly journals Relationship between the density distribution of intramembrane particles and electron transfer in the mitochondrial inner membrane as revealed by cholesterol incorporation.

1982 ◽  
Vol 94 (2) ◽  
pp. 387-393 ◽  
Author(s):  
H Schneider ◽  
M Höchli ◽  
C R Hackenbrock
Keyword(s):  
Electron Transfer ◽  
Surface Area ◽  
Lipid Bilayer ◽  
Average Distance ◽  
Membrane Lipid ◽  
Membrane Bilayer ◽  
Inner Membrane ◽  
Intramembrane Particles ◽  
Mitochondrial Inner Membrane ◽  
Membrane Lipid Bilayer

A low pH method of liposome-membrane fusion (Schneider et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:442) was used to enrich the mitochondrial inner membrane lipid bilayer 30-700% with exogenous phospholipid and cholesterol. By varying the phospholipid-to-cholesterol ratio of the liposomes it was possible to incorporate specific amounts of cholesterol (up to 44 mol %) into the inner membrane bilayer in a controlled fashion. The membrane surface area increased proportionally to the increase in total membrane bilayer lipid. Inner membrane enriched with phospholipid only, or with phospholipid plus cholesterol up to 20 mol %, showed randomly distributed intramembrane particles (integral proteins) in the membrane plane, and the average distance between intramembrane particles increased proportionally to the amount of newly incorporated lipid. Membranes containing between 20 and 27 mol % cholesterol exhibited small clusters of intramembrane particles while cholesterol contents above 27 mol % resulted in larger aggregations of intramembrane particles. In phospholipid-enriched membranes with randomly dispersed intramembrane particles, electron transfer activities from NADH- and succinate-dehydrogenase to cytochrome c decreased proportionally to the increase in distance between the particles. In contrast, these electron-transfer activities increased with decreasing distances between intramembrane particles brought about by cholesterol incorporation. These results indicate that (a) catalytically interacting redox components in the mitochondrial inner membrane such as the dehydrogenase complexes, ubiquinone, and heme proteins are independent, laterally diffusible components; (b) the average distance between these redox components is effected by the available surface area of the membrane lipid bilayer; and (c) the distance over which redox components diffuse before collision and electron transfer mediates the rate of such transfer.

scholarly journals Bespoke Biomolecular Wires for Transmembrane Electron Transfer: Spontaneous Assembly of a Functionalized Multiheme Electron Conduit

2021 ◽  
Vol 12 ◽  
Author(s):  
Samuel E. H. Piper ◽  
Marcus J. Edwards ◽  
Jessica H. van Wonderen ◽  
Carla Casadevall ◽  
Anne Martel ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Outer Membrane ◽  
Lipid Bilayer ◽  
Microbial Fuel Cells ◽  
Shewanella Oneidensis ◽  
Membrane Lipid ◽  
Electron Transfer Pathway ◽  
Redox Partners ◽  
Membrane Lipid Bilayer

Shewanella oneidensis exchanges electrons between cellular metabolism and external redox partners in a process that attracts much attention for production of green electricity (microbial fuel cells) and chemicals (microbial electrosynthesis). A critical component of this pathway is the outer membrane spanning MTR complex, a biomolecular wire formed of the MtrA, MtrB, and MtrC proteins. MtrA and MtrC are decaheme cytochromes that form a chain of close-packed hemes to define an electron transfer pathway of 185 Å. MtrA is wrapped inside MtrB for solubility across the outer membrane lipid bilayer; MtrC sits outside the cell for electron exchange with external redox partners. Here, we demonstrate tight and spontaneous in vitro association of MtrAB with separately purified MtrC. The resulting complex is comparable with the MTR complex naturally assembled by Shewanella in terms of both its structure and rates of electron transfer across a lipid bilayer. Our findings reveal the potential for building bespoke electron conduits where MtrAB combines with chemically modified MtrC, in this case, labeled with a Ru-dye that enables light-triggered electron injection into the MtrC heme chain.

scholarly journals PHLIP ARG-Mutant Interactions with the Membrane Lipid Bilayer

2021 ◽  
Vol 120 (3) ◽  
pp. 232a
Author(s):  
Hannah M. Visca ◽  
Oleg A. Andreev ◽  
Yana K. Reshetnyak
Keyword(s):  
Lipid Bilayer ◽  
Membrane Lipid ◽  
Membrane Lipid Bilayer

The Power of Asymmetry: Architecture and Assembly of the Gram-Negative Outer Membrane Lipid Bilayer

2016 ◽  
Vol 70 (1) ◽  
pp. 255-278 ◽  
Author(s):  
Jeremy C. Henderson ◽  
Shawn M. Zimmerman ◽  
Alexander A. Crofts ◽  
Joseph M. Boll ◽  
Lisa G. Kuhns ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Lipid Bilayer ◽  
Membrane Lipid ◽  
Gram Negative ◽  
Membrane Lipid Bilayer

scholarly journals Morphometric analysis of Leydig cells in the normal rat testis.

1980 ◽  
Vol 84 (2) ◽  
pp. 340-354 ◽  
Author(s):  
H Mori ◽  
A K Christensen
Keyword(s):  
Plasma Membrane ◽  
Surface Area ◽  
Morphometric Analysis ◽  
Leydig Cell ◽  
Leydig Cells ◽  
Steroidogenic Enzymes ◽  
Inner Membrane ◽  
Rat Testis ◽  
Mitochondrial Inner Membrane ◽  
Testis Tissue

Leydig cells are thought to be the source of most, if not all, the testosterone produced by the testis. The goal of this study was to obtain quantitative information about rat Leydig cells and their organelles that might be correlated with pertinent physiological and biochemical data available either now or in the future. Morphometric analysis of Leydig cells in mature normal rats was carried out on tissue fixed by perfusion with buffered glutaraldehyde, and embedded in glycol methacrylate for light microscopy and in Epon for electron microscopy. In a whole testis, 82.4% of the volume was occupied by seminiferous tubules, 15.7% by the interstitial tissue, and 1.9% by the capsule. Leydig cells constituted 2.7% of testicular volume. Each cubic centimeter (contained approximatelyy 1 g) of rat testis contained about 22 million Leydig cells. An average Leydig cell had a volume of 1,210 micron3 and its plasma membrane had a surface area of 1,520 micron2. The smooth endoplasmic reticulum (SER), the most prominent organelle in Leydig cells and a major site of steroidogenic enzymes, had a surface area of approximately 10,500 micron2/cell, which is 6.9 times that of the plasma membrane and is 60% of the total membrane area of the cell. The total surface area of Leydig SER per cubic centimeter of testis tissue is approximately 2,300 cm2 or 0.23 m2. There were 3.0 mg of Leydig mitochondria in 1 g of testis tissue. The average Leydig cell contained approximately 622 mitochondria, measuring on the average 0.35 micron in diameter and 2.40 micron in length. The mitochondrial inner membrane (including cristae), another important site of steroidogenic enzymes, had a surface area of 2,920 micron2/cell, which is 1.9 times that of the plasma membrane. There were 644 cm2 of inner mitochondrial membrane/cm3 of testis tissue. These morphometric results can be correlated with published data on the rate of testosterone secretion to show that an average Leydig cell secretes approximately 0.44 pg of testosterone/d or 10,600 molecules of testosterone/s. The rate of testosterone production by each square centimeter of SER is 4.2 ng/d or 101 million molecules/s: the corresponding rate for each square centimeter of mitochondrial inner membrane is 15 ng testosterone/d or 362 million molecules/s.

scholarly journals Anomalous behavior of water inside the SecY translocon

2015 ◽  
Vol 112 (29) ◽  
pp. 9016-9021 ◽  
Author(s):  
Sara Capponi ◽  
Matthias Heyden ◽  
Ana-Nicoleta Bondar ◽  
Douglas J. Tobias ◽  
Stephen H. White
Keyword(s):  
Membrane Proteins ◽  
Lipid Bilayer ◽  
Pyrococcus Furiosus ◽  
Hydrophobic Effect ◽  
Accessible Surface Area ◽  
Anomalous Behavior ◽  
Membrane Lipid ◽  
Nascent Chain ◽  
Membrane Lipid Bilayer ◽  
Dynamics Simulations

The heterotrimeric SecY translocon complex is required for the cotranslational assembly of membrane proteins in bacteria and archaea. The insertion of transmembrane (TM) segments during nascent-chain passage through the translocon is generally viewed as a simple partitioning process between the water-filled translocon and membrane lipid bilayer, suggesting that partitioning is driven by the hydrophobic effect. Indeed, the apparent free energy of partitioning of unnatural aliphatic amino acids on TM segments is proportional to accessible surface area, which is a hallmark of the hydrophobic effect [Öjemalm K, et al. (2011) Proc Natl Acad Sci USA 108(31):E359–E364]. However, the apparent partitioning solvation parameter is less than one-half the value expected for simple bulk partitioning, suggesting that the water in the translocon departs from bulk behavior. To examine the state of water in a SecY translocon complex embedded in a lipid bilayer, we carried out all-atom molecular-dynamics simulations of the Pyrococcus furiosus SecYE, which was determined to be in a “primed” open state [Egea PF, Stroud RM (2010) Proc Natl Acad Sci USA 107(40):17182–17187]. Remarkably, SecYE remained in this state throughout our 450-ns simulation. Water molecules within SecY exhibited anomalous diffusion, had highly retarded rotational dynamics, and aligned their dipoles along the SecY transmembrane axis. The translocon is therefore not a simple water-filled pore, which raises the question of how anomalous water behavior affects the mechanism of translocon function and, more generally, the partitioning of hydrophobic molecules. Because large water-filled cavities are found in many membrane proteins, our findings may have broader implications.

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