Biochimica et Biophysica Acta (BBA) - Biophysics including Photosynthesis最新文献

• 1.

  1. The fluorescence spectrum of photoconverted CP 668 shows a high peak at 747 nm and a much lower one at 676 nm.

• 2.

  2. From the action spectrum of 747-nm fluorescence it is concluded that, in aqueous solution, energy is transferred from CP 668 to CP 740.

• 3.

  3. The influence of KCN and β-mercaptoethanol (reagents breaking S-S linkages) on the fluorescence spectrum of photoconverted CP 668 and on the action spectrum of 747-nm fluorescence was investigated.

The original evidence for the operation of a “dimeriser” site in the human erythrocyte surface, in connection with facilitation of the passage of simple sugars through the cell membrane, has been experimentally re-examined and considerably extended. The course of total sugar uptake was followed photometrically, in mixtures of 21 pairs among nine monosaccharides, as a function of the varying proportions of the two sugars at a constant total level. The observed behavior was found to adhere closely to the quantitative predictions computed by numerical integration of rate equations derived from the simple monovalent carrier model proposed by Widdas, on the basis of previously estimated affinity constants for the various sugars, and a common rate constant for all.

The most crucial of Stein's dissonant conclusions from similar experiments, involving a systematic deviation of the initial cell swelling rates from this pattern, are shown to be accountable by errors inherent in the methods by which these data were analyzed. It is concluded that, although this type of experimental approach does not definitively exclude the possibility that the transport sites may be divalent for the substrate sugars, it provides no basis whatever for advancing this hypothesis.

The interaction between proflavine and the gel-forming deoxyribonucleohistone from calf thymus has been examined by means of the electrooptical method, in connexion with spectrophotometric, equilibrium dialysis and rigidity measurements, in media of very low ionic strenght.

• 1.

  1. The changes in the visible and ultraviolet proflavine spectra were similar to those already mentioned by different authors for DNA and soluble deoxyribonucleohistone-proflavine complexes at higher ionic strenght. Only two important differences were observed: the isosbestic point was absent in the visible spectra and a slight shift (± 5 mμ) of the ultraviolet absorption band of the dye to shorter wavelengths was noticed.

• 2.

  2. Binding curves showed an important interaction between proflavine and the gel-forming deoxyribonucleohistone in spite of the very low net electric charge of the macromolecule.

• 3.

  3. The complexes displayed a negative dichroism in the visible range, due entirely to the dye. The dichroic ratio D increased with decreasing numbers of ligand molecules bound per atom of phosphorus (r) and reached a maximum value of about 1.85 (for r ⩽ 0.10), approximately constant in the whole visible absorption band (field strength: 13–13.5 kV/cm).

• 4.

  4. At the same field strenght, the birefringence (B) at 550 mμ, per unit of gel-forming deoxyribonucleohistone concentration, increased towards a maximum value of about 1.45 dl/mg for r = 0.10.

• 5.

  5. The birefringence relaxation times τ were not noticeably affected by the interaction except for r > 0.10 where a decrease of τ was observed.

The results are consistent with an intercalation of the proflavine cations between adjacent nucleotide pairs, for at most one proflavine molecule per five nucleotide pairs in the gel-forming deoxyribonucleohistone. For higher proflavine contents, the dye molecules “in excess” would be externally attached to the helix.

Some comparative measurements on a soluble-deoxyribonucleohistone fraction were in agreement with this scheme.

The kinetics of the hydrolysis of ATP by a rat-brain lipoprotein fraction have been investigated. The activity is greatly increased in the presence of Na⁺ and K⁺, but reaches a maximum value and then suffers a diminution in the presence of an excess of either ion. Kinetic evidence indicates that these ions combine with the enzyme protein according to Michaelis-Menten kinetics, that 2 Na⁺ are involved in the activation, and that the interaction of Na⁺ and K⁺ at each site is of a competitive nature. Inhibition of the (Na⁺K⁺)-stimulated ATPase by ouabain, appears to result from a competition between ouabain and both K⁺ and Na⁺ while addition of oligomycin leads to kinetics which suggest competition of oligomycin with Na⁺. NH₄⁺ may substitute for K⁺ and, when present in excess, may also give rise to inhibitory effects.

• 1.

  1. The movements of I⁻ and other anions in Ehrlich ascites tumor cells were studied as a model to explain the restricted anion space of certain cells.

• 2.

  2. At 38° all the anions tested (I⁻, Br⁻, ReO₄⁻, WO₄²⁻) penetrate only one-quarter of the cell volume. For I⁻ this value, constant up to 6 h, is independent of the anion concentration in the medium from less than 1 μM to 0.124 M and is insensitive to anions that inhibit thyroidal I⁻ transport competitively.

• 3.

  3. At 4° the restriction of the I⁻ (and Br⁻) compartments (but not that of ReO₄⁻ or WO₄²⁻) is abolished and the I⁻ space approaches the water content of the cell. Upon exposure of the cold-loaded cells to 38°, a net efflux of the halide is observed until the steady-state value of one-quarter of the cell volume is again attained.

• 4.

  4. The temperature-dependent efflux of I⁻ is sensitive to various metabolic inhibitors, but, in ascites fluid, at a rather high concentration.

• 5.

  5. Cardiac glycosides and quinidine markedly decrease the ability of ascites cells to restrict the anion space. The same effect is produced by nucleoside triphosphates, particularly ATP, ITP and UTP.

• 6.

  6. The behavior of I⁻ and Na⁺ was compared under identical conditions. Although certain similarities exist, a number of differences were noted.

• 7.

  7. The evidence presented is consistent with the hypothesis that the halide restriction in ascites cells is due to a metabolism-dependent efflux.

The non-rotational hydration of DNA and its correlation time have been investigated by the NMR spin-echo technique. Relaxation times T₁ and T₂ were measured at 20° and the dependence of the values of T₁ and T₂ on the DNA concentration was established. The theory of this phenomenon is discussed. The non-rotational amount of water was shown to be dependent on the molecular weight of the DNA, ranging from about 8 to 10% with molecular weights of 6·10⁶ to 7·7·10⁶. The non-rotational hydration represents only a part of the total water present in hydration shells. Denaturation of the DNA decreases the non-rotational hydration 1.45 times as compared with native DNA simultaneously resulting in an increase in the correlation time, τ_c, by a factor of 1.45. Denatured DNA molecules have distinctly less freedom of movement than double-helix DNA which has a high degree of structural organization.

• 1.

  1. In the presence of Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ have an activating effect on the ATPase activity of human red-cell ghosts, the greatest activity being obtained with Sr²⁺ as the activator.

• 2.

  2. The presence of Ca²⁺ and Sr²⁺ tends to prevent the activation by Na⁺ and K⁺.

• 3.

  3. The activating effects of Mg²⁺ and Ca²⁺ appear to differ in their point of attack; Sr²⁺ and Ba²⁺ seem to be bound by the same sites as Ca²⁺.

• 4.

  4. There is an optimal ratio between the concentrations of Mg²⁺ and Ca²⁺ (or Sr²); excess Ca²⁺ (or Sr²⁺) has an inhibiting effect, presumably by interfering with Mg²⁺ activation. Excess Mg²⁺ may also interfere with Ca²⁺ (or Sr²⁺) activation.

• 5.

  5. The optimal pH is somewhat higher for the (Na⁺ + K⁺)-dependen activity than for the (Mg²⁺ + Ca²⁺)-dependent activity and the curves of the activity as a function of pH have different shapes.

• 6.

  6. The (Mg²⁺ + Ca²⁺)-dependent activity is inhibited by Salygran, Atebrin and more specifically by sodium Amytal and 2,4-dinitrophenol. In the presence of Mg²⁺ alone, the ATPase activity is inhibited by Atebrin, Salygran and, more specifically, by guanidin. The (Mg²⁺ + Na⁺ + K⁺)-dependent component is inhibited by Atebrin and Salyrgan but is insenstivie to guanidin and 2,4-dinitrophenol.

• 7.

  7. The properties of the (Mg² + Ca²⁺)-dependent enzymic system are analogous to those of myofibrillar ATPase; thus, this system may be identified with the actomyosin-like proteins described in red-cell ghosts by Ohnishi.

• 8.

  8. In the presence of 2,4-dinitrophenol in amounts sufficient to inhibit the (Mg²⁺ + Ca²⁺)-dependent ATPase, one observes in intact cells a marked increase in the passive permeability to Na⁺ but no effect on active transport. This suggests that contractile proteins of red cells may be involved in the regulation of passive permeability to Na⁺.