Aggregation of tyrocidine in aqueous solutions.

The formation of aggregates of tyrocidine B at 4°C and 20°C in aqueous solutions was studied by means of light scattering and fluorescent techniques. The apparent weight molecular weight of tyrocidine B aggregates was found to be 36,000 at 4°C and 28,800 at 20°C. Fluorescence titration experiments with dansyl-chloride resulted in an aggregational number of 31 (4°) and 28 (20°) indicating that one molecule of dye is bound per monomer of molecular weight 1,200. From a Scatchard plot apparent association constants of 1.22 × 10⁵ M (4°) and 0.95 × 10⁵ M (20°) were calculated. From the angular dependence of scattered intensity the radii of gyration were determined to be 60 Å and 58 Å, respectively.     

Reactive oxygen species generated by the mitochondrial respiratory chain affect the complex III activity via cardiolipin peroxidation in beef-heart submitochondrial particles

The aim of this study was to investigate the effect of reactive oxygen species (ROS), produced by the mitochondrial respiratory chain, on the activity of complex III and on the cardiolipin content in bovine-heart submitochondrial particles (SMP). ROS were produced by treatment of nicotinamide adenine dinucleotide (NADH) respiring SMP with rotenone. This treatment resulted in a production of superoxide anion, detected by the epinephrine method, which was blocked by superoxide dismutase (SOD). Exposure of SMP to mitochondrial-mediated ROS generation resulted in a marked loss of complex III activity and in a parallel loss of mitochondrial cardiolipin content. Both these effects were completely abolished by SOD + catalase. Exogenous added cardiolipin was able to almost completely prevent the ROS-mediated loss of complex III activity. No effect was obtained with other major phospholipid components of the mitochondrial membrane such as phosphatidylcholine and phosphatidylethanolamine, or with peroxidized cardiolipin. The results demonstrate that mitochondrial-mediated ROS generation affects the activity of complex III via peroxidation of cardiolipin, which is required for the functioning of this multisubunit enzyme complex. These results may prove useful in probing molecular mechanisms of ROS-induced peroxidative damage to mitochondria, which have been proposed to contribute to those physiopathological conditions characterized by an increase in the basal production of ROS such as aging, ischemia/reperfusion and chronic degenerative diseases.     

Crystallographic study of single crystals of mitochondrial coupling factor (BF1) from beef heart

Beef heart mitochondrial coupling factor (BF₁) was crystallized from 0.1 M Tris-PO₄, pH 7.8, containing 1 mM EDTA, 4 mM ATP and 1.85 M (NH₄)₂SO₄, at 22°C. Single crystals were obtained different from those reported by Spitzberg and Haworth (Biochim. Biophys. Acta 492, 237–240, 1977). The X-ray diffraction pattern reveals an orthorhombic lattice with a = 150 Å, b = 132 Å and c = 180 Å and, according to the absence of reflection, a space group of C222₁. The crystal density was determined to 1.19 g·ml^?1 and, assuming a molecular weight of 350,000 for BF₁, there is only one half of the BF₁ molecule in the asymmetric unit cell.     

Solution properties of a cell wall protein fromAcetabularia (Polyphysa) cliftonii

Summary Studies have been performed on the precipitation of a cell wall protein, isolated from the marine green algaAcetabularia, from dilute aqueous solutions over the pH range where the -helical conformation is maintained. The major purpose of this study was to establish the molecular conformation of a naturally occurring polypeptide of a molecular weight of 14,000 in the precipitate and to outline the mechanism of the precipitation. Since the precipitation behaviour from homogeneous protein solutions is important in relation to solution properties of the cognate polysaccharide chain from this alga, it was necessary to investigate the different conformations of the cell wall protein, including the possible aggregational states. Utilizing molecular weight fractions it can be shown that there are two distinctly different precipitation regions that depend on temperature, concentration of the protein, and pH. In one of these regions, the so-called -region, precipitation occurs only in the -helical conformation, without any conformational change if the physical conditions are varied. The temperature coefficient of the precipitation process in this -region indicates that it must be nucleation controlled.     

Induction of ethylene formation in bean (Phaseolus vulgaris) hypocotyl segments by preparations isolated from germ tube cell walls of Uromyces phaseoli

Hypocotyl segments of Phaseolus vulgaris produce ethylene at pH 8.0 and ethane at pH 5.4. Ethylene formation, but not ethane formation, was stimulated by methionine, while -linolenic acid stimulated both ethylene and ethane formation. Detached primary leaves of var. Favorit (susceptible to Uromyces phaseoli) show no enhanced ethylene formation, whereas primary leaves from var. 017 (hypersensitive) exhibit two distinct ethylene peaks ca. 10 h and 50 h after inoculation with U. phaseoli.Cell wall preparations from uredospore germ tubes of U. phaseoli strongly stimulate ethylene formation in hypocotyl segments of the hypersensitive var. 017 but to a much lesser extent in the susceptible var. Favorit.Abbreviation UCP Uromyces Cell Wall Preparation