Oxidative Conformational coupling

The spatial separation between the components of the electron transport chain and the site of ATP synthesis was incompatible with simple interpretations of the chemical coupling hypothesis. In 1964, Paul Boyer suggested that conformational changes in components in the electron transport system consequent to electron transfer might be coupled to ATP formation, the conformational coupling hypothesis. No evidence for direct association has been forthcoming but conformational changes in the subunits of the FI particle are now included in the current mechanism for oxidative phosphorylation. 

The observation that T0 for PVN has disappeared, as shown by examining both the damping constant and the dilatometric curve, unequivocally shows that PVN has lost its identity and that the whole copolymer behaves as an entity. The specific volume for temperatures in the amorphous region (above 60°C.) show that volume additivity for the two components is not followed, but that a contraction of about 2% has taken place. Examining the molecular models shows that one can readily entwine PEO and PVN chains. Optimum spacing is obtained with 3 ethylene oxide 1 naphthalene moiety—the complex composition Thus here, as with polyblends, the importance of conformation coupled with favorable but probably weak interactions is evident. 

Methods presently employed for obtaining correctly refolded proteins from inclusion body preparations are often all-or-none propositions. They typically consist of denaturant solubilization, in urea or guanidine, followed by dilution or dialysis (2). Recovery of native activity or structure may be aided by using additives (enzyme inhibitors, co-factors, oxidation-reduction couples, etc.), which act to stabilize the native-state protein conformation. However, because such efforts are time-consuming and tedious, systematic examinations of solution conditions for protein folding/unfolding are rarely performed. 

Chemiosmotic and Conformational Coupling Fatty Acid Oxidation 54 Acyl Dehydrogenases Crotonase... 

Throughout this discussion of oxidative phosphorylation, we have assumed that the coupling mechanisms involve the formation of high-energy intermediates. This chemical hypothesis is not accepted by all the chemiosmotic hypothesis of oxidative phosphorylation was proposed by Mitchell in 1961, and in 1966 Boyer [148] proposed a new hypothesis involving conformation coupling. 

Much investigative effort has been directed towards the elucidation of the coupling of the two aspects of oxidative phosphorylation. Historically, three mechanisms have been proposed the chemical coupling hypothesis, the chemiosmotic hypothesis and conformational coupling hypothesis. 

A similar situation exists in the hydroxymercuration and thallium(m) oxidation of cycloalkenes and cycloalkanes, the rate laws showing strict second-order behaviour for both metal ions. In the thallium(ni) reactions two products have been observed, a 1,2-diol and a ketone or aldehyde. Two-electron coupling with trifluoroacetate has been shown to promote oxidative phenol coupling. The mechanism of oxidation of olefins by palladium(n) has been investigated. In the presence of PdClg in aqueous media, the data conform to the rate expression... 

Based on NMR chemical shift assignments and the use of recorded spin-spin coupling constants it was determined193 that in both 2,4-diphenyl-substituted thietane oxides (186a,b) the dominant conformers are those in which the S—O bond is equatorial and, therefore, in the trans-2,4-isomer186 one phenyl group (i.e. R1) is syn-axial to the S— O bond, whereas in the cis-2,4-diphenyl isomer 186b both phenyls are anti-equatorial to the S—O bond. 

The ESR spectrum of the thioxanthene S, S-dioxide radical anion itself shows that the two possible conformers coexist, since the two methylene protons are not equivalent. In the case of the 9-monoalkyl derivatives, the large coupling constant observed for the 9-proton leads to the conclusion that the 9-substituent is in the boat equatorial position as in II1 F Thus the radical anions and the neutral molecule display different conformations. The protons in the 9-position of the radical anions of cis-9-methylthioxanthene S-oxides (2, n — 1, R1 = H, R2 = CH3) have an appreciable coupling constant10 which suggests that these radical anions have the substituent in the pseudo-axial position. Furthermore, in the radical anions the S—O bond is pseudo-axial. These situations are exactly the opposite of that observed for the neutral compound. 

It is difficult to decide whether the discrepancy between the calculated and experimental data is due to a different conformational preference of the thietane dioxides in the liquid and the solid phase, or to the crude approximations included in the Karplus-Barfield equation. However, the relationship between vicinal coupling constants and dihedral angles appears qualitatively valid in thietane oxides and dioxides, particularly if trends instead of exact values are discussed . At any rate thietane dioxides, 1,3-dithietane dioxides and tetroxides maintain either planarity or a slightly distorted average vibrating conformation with a low barrier to ring planarity . 

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