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

The effect of nicotine and the pH dependence of its potency were tested on the monocellular electroplax preparation of Electrophorus.

• 1. Nicotine (5·10⁻⁵M) blocks the action potential reversibly within 5 min. The stepwise depolarization of the membrane by increasing concentrations is shown.

• 2. Curare inhibits the effect of nicotine. Both compounds act at the synapse only. The mode of action is competitive. In contrast, the toxin obtained from clam affects the preparation without interference with the effect of nicotine.

• 3. Increasing the pH from 6.2 to 9.0 decreases the potency of nicotine by a factor of 2–3 and, in addition, increases the time required for reaching the equilibrium potential by a factor of 5–10.

• 4. The degree of ionization of nicotine has been evaluated in relation to potency of action.

The “red complex” formed at pH 11 from poly-α, l-lysine (up to 10⁻² monomolar) and ferriheme (10⁻⁴−10⁻⁵M) has been investigated by absorption spectrophotometry in the range 270–650 mμ. This complex was not formed by oligopeptides of l-lysine (p⩽ 5) under analogous conditions. The complex, which was formed at high ratios of lysine residues/ferriheme, had its maximum absorption at pH 11. NaBr below 10⁻² M had no measurable effect on absorption of the complex in the visible range while higher concentrations of salt (0.7 M NaCl) caused significant changes in the spectrum of the complex formed with low-molecular-weight poly-l-lysine. The absorption of the red complex was found to depend on the molecular weight of the poly-l-lysine. Spectrophotometric titrations between ferriheme and poly-l-lysine are described. Reversible spectral changes were observed, at higher temperatures, which are attributed to excessive changes in the secondary structure of the polypeptide. On the basis of spectral and conformational relationships and with previous stereo-chemical data, a likely structure for the synthetic complex involving helical polypeptide is reviewed. On account of its classification as a low-spin ferrihemochrome, spectral and magnetic data for the red polylysine complex are compared with those for similar compounds, including ferricytochrome c.

An electron-microscope study has been made of elastoidin from Cetorhinus maximus. Longitudinal, cross and oblique sections of permanganate-stained material have been studied.

Longitudinal sections show an extremely regular banding. The bands extend apparently over the entire width of the fibres. The same pattern of three dark stained lines occurs in all of the sections studied.

Oblique sections show a larger but less well defined period.

Cross and, indeed, the longitudinal and oblique sections have a granular appearance at the highest magnifications.

These electron-microscope observations are discussed in relation to other electron-microscope and X-ray work.

Aspidistra elatior chloroplasts are treated with buffer to which acetone of various concentrations is added.

Upon replacement of the solvent-containing medium by buffer, it appears that acetone concentrations up to about 40% produce a reversible shift of the main absorption maximum to the short-wave side. With higher concentrations, such a shift is, least partially, irreversible. The magnitude of this shift proceeds linearly with acetone concentration.

Acetone in concentrations lower than about 50% most probably solubilizes chlorophyll-protein complexes. The position of the main absorption maximum of these complexes in the acetone-containing medium is shifted to the short-wave side, whereas, also in this case, the magnitude of the shift is dependent on the applied solvent concentration.

At least some of the individual chlorophyll a types are extracted by acetone of various concentrations at mutually different rates. The latter result stresses the individuality of these chlorophyll a types.

• 1. The optical rotatory properties of four purified samples of human 19-S γ-globulin have been studied in detail.

• 2. The dispersion constants of the protein and the changes in the optical rotatory behaviour in polar and non-polar solvents are found to resemble those of 7-S γ-globulin.

• 3. It is suggested that the behaviour is compatible with the presence of β-form and right-handed α-helix in th molecule.

The dielectric dispersion of bovine serum albumin and ovalbumin was studied before and after urea denaturation. Native bovine serum albumin was found to have an exceedingly small dielectric increment indicating that the charge distribution in this protein has a remarkably high degree of symmetry. The dielectric increment and the relaxation time increase on the addition of high concentration of urea. However, the dielectric properties of denatured bovine serum albumin are not drastically different from that of native protein indicating that urea denatured bovine serum albumin still maintains considerably large amounts of original folding of peptide chains. In contrast to bovine serum albumin, ovalbumin undergoes more pronounced change in the dielectric properties but it is more likely due to the formation of aggregates after urea denaturation, rather than the unfolding of peptide chain in individual molecules.