Biochimica et Biophysica Acta (BBA) - Specialized Section on Biophysical Subjects最新文献

It has been shown that electron-acceptor quinones can complex to proteins, decreasing their electrical resistivity and semiconductive activation energy. Such complex proteins are suitable for energy transport in biological systems by a semiconduction mechanism.

Coenzyme Q₁₀ is known to be involved in oxidative phosphorylation reactions in association with the cytochrome system. The semiconductive and optical properties of a cytochrome c-coenzyme Q₁₀ complex have indicated a possible mechanism for such reactions and an investigation of this complex in a mitochondrial lipid medium and complete mitochondria has provided evidence for the possible role of a semiconductive mechanism in mitochondrial energy transport.

Collagen fibres have been reconstituted by warming neutralised collagen solutions in the presence of various relevant substances, and their ease of dispersion in KI and urea subsequently determined. Of the substances which appeared to inhibit resolubilisation of the fibres, a particular study was made of salts and amino acids. Anion and cation series were obtained showing the relative effect of ions, which is probably a consequence of their salting-out potency. All the amino acids tested had a similar, weakly inhibiting effect on fibre redispersion. Kinetic studies showed that the amino acids stabilise the soluble collagen against precipitation but that the fibres once formed are less easily dispersed than controls. The inhibition of dispersion by serine is maximal at pH 6.5 and it is postulated that under these condition the charge properties of the two ampholytes are summated in such a way that non-specific cross-linkage during fibre formation is suppressed, allowing the formation of specific cross-links. It cannot be assumed that similar effects operate in vivo, but it is obvious that every simple connective-tissue components may quite markedly influence the properties of collagen fibres.

The tyrocidines A, B and C, which are cyclic decepeptides, can be adsorbed layers 150–250 Å thick on metallized glass slides coated with a few monolayers of the barium salts of high homologs of straight-chain fatty acids. There is a sharp transition temperature for each fatty acid below which no adsorption occurs and above which a thick layer of tyrocidine can be adsorbed. The transition temperatures increase with the length of the chain of the acid by 3–3.5° per additional carbon atom in the chain. The range of the transition temperatures covers an interval of roughly 30°, from a few degrees centigrade for myristic acid to over 30° for ligoceric acid. A transition point can be considered as a pseudo melting point. Tyrocidine can be adsorbed in spite of a protective membrane deposited on the fatty acid layers. If the membrane consists of two layers of a longer fatty acid whose transition temperature is higher than the temperature at which the adsorption is carried out, an adsorption nevertheless takes place above a certain temperature which is intermediate between the temperature of transition of the underlying shorter acid and that of the longer acid used for the membrane. Cooperative phenomena involving many of the successive layers deposited on the slide play a role in these interactions.

• 1.

  1. Slices of denatured protein gels and cortical slices from the kidneys of adult rats were subjected to equivalent experimental conditions in order to determine the factors promoting selective K⁺ accumulation.

• 2.

  2. The addition of polythelene glycol 6000 to the medium decreased the water content of rat kidney cortex slices at 0° and at 38°, and was used to control swelling at low concentrations of ions.

• 3.

  3. K⁺ selectivity of slices of gel at 20° and of anaerobic tissue at 38° incubated in media of constant composition decreased as the water content increased.

• 4.

  4. K⁺ selectivity of slices of gel at 20° and of kidney cortex incubated both at 0° and anaerobically at 38° increased as the concentrations of Na⁺ and K⁺ in the medium were decreased whilst the Na⁺/K⁺ ratio and the water content of the slices were held constant.

• 5.

  5. K⁺ selectivity of slices of gel at 20° and of kidney cortex incubated anaerobically both at 38° and at 0° increased as the relative concentration of K⁺ in the medium decreased whilst the sum of the concentrations og Na⁺ and K⁺ in the medium and the water content of the slices were held constant.

• 6.

  6. These results have been interpreted in terms of a model first proposed for ion- exchange resins. It has been shown that with further assumptions the model could account for the asymmetric distribution of Na⁺ and K⁺ in respiring tissue, and for the swelling, uptake of Na⁺ and loss of K⁺ that occur with anoxia at 38° or on chilling to 0°.

The carotenoid pigments of Euglena gracilis were studied following illumination of the cells under aerobic and anaerobic conditions. Cells harvested from cultures in the stationary phase displayed a photochemical conversion of epoxide carotenoids to non-epoxide pigments under anaerobic conditions. This reaction was reversed in the dark and could be inhibited by aerobiosis. Analysis of the individual pigments indicated that the following reaction was occurring: