Systematically Creased Thin-Film Membrane Structures

This paper presents a study of a square membrane, creased according to the Miura-ori folding pattern. When the membrane is allowed to expand from its packaged configuration, it initially expands elastically under zero corner forces. Starting from this naturally expanded configuration, the paper investigates the stress distribution and the load-displacement relationship when in-plane, diagonal loads are applied at the corners. It is found that out-of-plane bending is the main load-carrying mode and, for stress magnitudes typical of current solar-sail designs, the behavior of the membrane remains linear elastic. A simple analytical model, originally proposed for randomly creased membranes, is shown to predict with good accuracy the load-displacement relationship of the corners. It uses physically based and hence directly measurable membrane parameters

The NDUFS4 nuclear gene of complex I of mitochondria and the cAMP cascade

AbstractResults of studies on the role of the 18 kDa (IP) polypeptide subunit of complex I, encoded by the nuclear NDUFS4 gene, in isolated bovine heart mitochondria and human and murine cell cultures are presented.The mammalian 18 kDa subunit has in the carboxy-terminal sequence a conserved consensus site (RVS), which in isolated mitochondria is phosphorylated by cAMP-dependent protein kinase (PKA). The catalytic and regulatory subunits of PKA have been directly immunodetected in the inner membrane/matrix fraction of mammalian mitochondria. In the mitochondrial inner membrane a PP2Cγ-type phosphatase has also been immunodetected, which dephosphorylates the 18 kDa subunit, phosphorylated by PKA. This phosphatase is Mg2+-dependent and inhibited by Ca2+. In human and murine fibroblast and myoblast cultures “in vivo”, elevation of intracellular cAMP level promotes phosphorylation of the 18 kDa subunit and stimulates the activity of complex I and NAD-linked mitochondrial respiration.Four families have been found with different mutations in the cDNA of the NDUFS4 gene. These mutations, transmitted by autosomal recessive inheritance, were associated in homozygous children with fatal neurological syndrome. All these mutations destroyed the phosphorylation consensus site in the C terminus of the 18 kDa subunit, abolished cAMP activation of complex I and impaired its normal assembly

The allosteric protein interactions in the proton-motive function of mammalian redox enzymes of the respiratory chain

Insight into mammalian respiratory complexes defines the role of allosteric protein interactions in their proton-motive activity. In cytochrome c oxidase (CxIV) conformational change of subunit I, caused by O2 binding to heme a32+-CuB+ and reduction, and stereochemical transitions coupled to oxidation/reduction of heme a and CuA, combined with electrostatic effects, determine the proton pumping activity. In ubiquinone-cytochrome c oxidoreductase (CxIII) conformational movement of Fe-S protein between cytochromes b and c1 is the key element of the proton-motive activity. In NADH-ubiquinone oxidoreductase (CxI) ubiquinone binding and reduction result in conformational changes of subunits in the quinone reaction structure which initiate proton pumping

The effect of mild trypsin digestion of F1 on energy coupling in the mitochondrial ATP synthase

AbstractMild trypsin digestion of isolated bovine-heart mitochondrial F1-ATPase removed the first 15 residues from the N-terminus of subunit a under conditions in which other F1 subunits were apparently untouched. When the trypsinized F1 (TF1) was reconstituted with the F0 sector in the mitochondrial membrane (USMP), the ATP hydrolase activity acquired oligomycin sensitivity but ATP hydrolysis was decoupled from proton pumping. TF1 added to USMP did not block the proton channel in F0 as the native F1 did. AMP-PNP inhibited proton conductivity in reconstituted F1-USMP but this effect was lost in reconstituted TF1-USMP. These results indicate that the N-terminus of the F1 α subunit plays a critical role in the conformational communication between F1 and F

Cooperativity and flexibility of the protonmotive activity of mitochondrial respiratory chain

AbstractFunctional and structural data are reviewed which provide evidence that proton pumping in cytochrome c oxidase is associated with extended allosteric cooperativity involving the four redox centers in the enzyme . Data are also summarized showing that the H+/e− stoichiometry for proton pumping in the cytochrome span of the mitochondrial respiratory chain is flexible. The ΔpH component of the bulk-phase membrane electrochemical proton gradient exerts a decoupling effect on the proton pump of both the bc1 complex and cytochrome c oxidase. A slip in the pumping efficiency of the latter is also caused by high electron pressure. The mechanistic and physiological implications of proton-pump slips are examined. The easiness with which bulk phase ΔpH causes, at least above a threshold level, decoupling of proton pumping indicates that for active oxidative phosphorylation efficient protonic coupling between redox complexes and ATP synthase takes place at the membrane surface, likely in cristae, without significant formation of delocalized ΔμH+. A role of slips in modulating oxygen free radical production by the respiratory chain and the mitochondrial pathway of apoptosis is discussed

Disulfide cross-linking of subunits F1-γ and F0I-PVP(b) results in asymmetric effects on proton translocation in the mitochondrial ATP synthase.

AbstractA study is presented on the effect of diamide-induced disulfide cross-linking of F1-γ and F0I-PVP(b) subunits on proton translocation in the mitochondrial ATP synthase. The results show that, upon cross-linking of these subunits, whilst proton translocation from the A side to the B F1 side is markedly accelerated with decoupling of oxidative phosphorylation, proton translocation in the reverse direction, driven by either ATP hydrolysis or a diffusion potential, is unaffected. These observations reveal further peculiarities of the mechanism of energy transfer in the ATP synthase of coupling membranes

Inhibition of proton pumping in membrane reconstituted bovine heart cytochrome c oxidase by zinc binding at the inner matrix side

AbstractA study is presented on the effect of zinc binding at the matrix side, on the proton pump of purified liposome reconstituted bovine heart cytochrome c oxidase (COV). Internally trapped Zn2+ resulted in 50% decoupling of the proton pump at level flow. Analysis of the pH dependence of inhibition by internal Zn2+ of proton release in the oxidative and reductive phases of the catalytic cycle of cytochrome c oxidase indicates that Zn2+ suppresses two of the four proton pumping steps in the cycle, those taking place when the 2 OH− produced in the reduction of O2 at the binuclear center are protonated to 2 H2O. This decoupling effect could be associated with Zn2+ induced conformational alteration of an acid/base cluster linked to heme a3

Vectorial nature of redox Bohr effects in bovine heart cytochrome c oxidase

AbstractThe vectorial nature of redox Bohr effects (redoxlinked pK shifts) in cytochrome c oxidase from bovine heart incorporated in liposomes has been analyzed. The Bohr effects linked to oxido-reduction of heme a and CuB display membrane vectorial asymmetry. This provides evidence for involvement of redox Bohr effects in the proton pump of the oxidase