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

Rapid absorption changes can be induced by short light flashes in Ochromonas danica. The absorption change rises in 10⁻⁴ sec or less and has a half life of 35–40 msec. The complex difference spectrum has positive peaks at 443, 475, 505 and 580 mμ and negative peaks at 490 and 535 mμ.

The absorption change is very sensitive to physical treatments. Heating to 40° for 2 min or sonicating at 10 kcycles for 1 sec completely eliminates the signal.

The absorption change remains unaffected by resuspending the organism in a “starvation” medium or by making the medium anaerobic. The presence of several oxidants or reductants, KCN, and iodoacetamide has no noticeable effects on the absorption changes.

3-(3,4-dichlorophenyl)-1,1-Dimethylurea at 10⁻⁷ and 10⁻⁶M reduces the magnitude of the absorption change by 50 and 75%, respectively. A residual activity (about 20%) persists up to 0.5 mM 3-(3,4-dichlorophenol)-1,1-dimethylurea. 2,4-Dinitrophenol reduces the absorption change and accelerates the decay, whereas carbonyl cyanide m-chlorophenylhydrazone only lengthens the decay. H₂O₂ both reduces the magnitude of the absorption change and lenghtens the decay.

A former study of chlorophyll fluorescence in Chlorella had lead to the distinction of several fractions of the chlorophyll holochrome: A photoreceptive fraction Chl₀ and two fractions Chl₁⁶⁸⁵ and Chl₁⁷²⁰ the excition of which was sensitized by the first one. The Chl₁⁶⁸⁵ fraction has a potochemical function and is responsible for the variable yield emission. The constant yield emission maily comes from Chl₀ and to a lesser extent from Chl₁⁷²⁰.

By studies of fluorescence polarisation, this scheme of excitation transfers is confirmed; moreover, the Chl₁⁷²⁰ fraction has a certain amount of direct absorption and a high degree of orientation.

The variation of fluorescence yield during the induction period is seen as resulting from the distribution of the Chl₁⁶⁸⁵ fraction between at least two forms: the non-fluorescent O form and the fluorescent P form. Action spectra of the Chl₁⁶⁸⁵ show in the far red a difference between the photochemical production of the P form and the excitation of its fluorescence. This difference can be understood in the theory of two photochemical systems of photosynthesis as resulting from the antagonistic action of each system on the P form.

The general scheme of electron transport in photosynthesis and the concept of structural separation of the sensitizers of the two systems are discussed.

Purified tubular membranes prepared by extracting rat skeletal muscle cell fragments with buffered 0.4 M LiBr solution have been shown by electron microscopy to retain the major three layers (outer network of collagen fibrils, middle basement membrane, and inner plasma membrane) of the sarcolemma of the intact muscle cell. A chloroformmethanol mixture destroyed the plasma membrane, thereby extracting steroid, glyceride, phosphatide, protein and carbohydrate. A collagenase (EC 3.4.4.19) preparation appeared to digest not only the collagen network, but also the basement membrane. The lipid extractio or collagenase treatment did not destroy the tubular structure of the isolated membrane, but successive application of both treatments yielded only an amorphous precipitate.

• 1.

  1. Data on the separation of mitochondrial and microsomal fractions from rat liver by density-gradient electrophoresis with and without electrolyte gradients are described. Physiological cations were deliberately excluded from the system. The theoretical basis of electrophoresis in density and electrolyte gradients is discussed.

• 2.

  2. A mitochondrial fraction prepared in the presence of EDTA is shown to consist principally of mitochondria and other particles which are probably nuclear fragments.

• 3.

  3. Microsomes (glucose 6-phosphatase particles) have been separated from ferritin, and by means of electrophoresis on an electrolyte gradient a complex charge distribution has been demonstrated for microsomes. Other minor components are present.

A diffusion method is described for visualization of DNA molecules which is equivalent to the spreading of a mixed DNA-protein solution. Macromolecules diffusing in a solution of about 5×10⁻⁸ g DNA per ml are adsorbed by a cytochrome c-film at the air-water interface. Subsequently they are transferred to electron microscopic supports. In the enlarged two-dimensional image the end-to-end distances and the length distribution are measured for different DNA preparations (from cod fish, trout, holothuria and T₂ phage). Following recalculation in the three-dimensional state a relation is given for the mean square of the end-to-end distances, $\text{h}{}^2$, and the length, L, as $\text{(}\text{h}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 1.3 × 10}{}^{\mathrm{-1}}\text{L(1 + √}\text{1 + 2.3 × 10}{}^{\mathrm{-3}}\text{L}$ at ionic strengths from 0.09 to 0.35, according to a theory by Katchalsky and Lifson for diluted linear polyelectrolytes. The molecular shape is not a random coil or a rod but intermediate on account of electrostatic interaction. An application of the results on the theory of Kuhn, Kuhn and Buchner yields equations for the diffusion coefficient or other characteristics of DNA as a function of length or molecular weight. The length distribution of DNA, after disintegration by preparation and storage, usually has the form of a descending exponential function. Within the accuracy of the length distribution it is allowed to deduce random scissions along the native DNA molecule.

The cyclic increases and decreases of fluorescence emission of slices of the main organ of Electrophorus electricus which have been interpreted as DPN⁺ reduction at the glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) site are here correlated with assays of essential intermediates of glycolysis. Large increases of fructose 1,6-diphosphate, glyceraldehyde 3-phosphate, 3-phosphoglyceric acid and 2-phospholgyceric acid are found to occur at the time of the maximum increases of fluorescence and to have subsided as the flourescence increase subsides. Measurements of increased DPN concentration and glyceraldehyde 3-phosphate concentration identify the fluorescence increase with DPN⁺ reduction at glyceraldehyde-3-phosphate dehydrogenase. The activation of glycolysis appears to be due to a concentrated effect of increased ADP and creased ATP concentration upon phosphofructokinase (EC 2.7.1.11), 1,3-diphosphojlycerate kinase (EC 2.7.2.3) and glyceraldehyde-3-phosphate dehydrogenase. The possibility of other activators of phosphofructokinase is also to be considered.

Anomalous diffraction spectra of monolayers of biological cells dried on a quartz plate were observed between 0.25 and 2.5 μ. The possibility of using the positions of the diffraction maxima and minima for the determination of cell dimensions was examined on the basis of a simple theory of anomalous diffraction for spherical or discoidal cells. In the spectra region used, yeast and Chlorella cells showed two diffraction maxima, and spinach chloroplasts and human erythrocytes a single maximum. The relative wavelengths of the two maxima and the minimum between them were in the ratios calculated from the theory, so that it was possible to evaluate a term proportional to the cell diameter or thickness. The proportionality between the evaluated quantity and the diameter was examined with yeast, Chlorella cells, cloroplasts, and erythrocytes, and was approximately constant. A semi-empirical formula for the determination of cell dimensions was obtained by assuming the average of the proportionality constants for these different species of cells. The maximum error due to this assumption and due to the variation of the content of solid materials in cells was estimated to be 13% in diameter. The diffraction method was compared with other optical or microscopic methods for the determination of cell dimensions.

For Archibald molecular weight calculations measurements are made along a single Rayleigh fringe. The displacement of the fringe measured as a function of the radial distance, x, is used to obtain the concentration gradient dc/dx by fitting a second-degree polynomial in x, extrapolating and differentiation. Good agreement with published values of the molecular weight was obtained with solutions of RNAase and of bovine serum albumin.

Also described is a graphical method for obtaining dc/dx from a tangent to the fringe drawn upon a photographic enlargement.