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

• 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⁺.

Illuminated spinach chloroplasts reduce quarternary dipyridyl salts with oxidation-reduction potentials ranging from −342 to −656 mV. The accumulation of reduced dipyridyl was dependent upon the oxidation-reduction potential of each dipyridyl, ranging from 100% with the 1,1′-ethylene-2,2′-dipyridylium dibromide (E₀′ = −342 mV) to 3% with the 1,1′-trimethylene-2,2′-dipyridylium-4,4′-methyl dibromide (E₀′ = −656 mV). The data suggest that the oxidation-reduction potential of a natural photosynthetic reductant(s) may be near −521 mV. Photosynthetic phosphorylation occurs concurrent with reduction under both argon and air. In the presence of oxygen the reduced dipyridyls are oxidized and H₂O₂ is produced. The dipyridyls could be substituted for spinach ferredoxin in a dark reduction of cytochrome c in the presence of NADPH and NADP⁺ reductase (EC 1.6.99.4). The polagraphic half-wave oxidation-reduction potential of the dipyridyls is reported.

• 1.

  1. Incubation of isolated rat hemidiaphragm in a K⁺-free bicarbonate buffer has been shown to induce stimulation of glycogen synthesis and inhibition of lactate production, without change in glucose uptake.

• 2.

  2. Essentially similar changes were produced when ouabain was added to bicarbonate buffer with a normal K⁺ content.

• 3.

  3. These metabolic changes were therefore considered as secondary to a decrease in active cation transport.

• 4.

  4. Insulin (0.1 I.U./ml) was shown to stimulate glycogen synthesis, lactate production and glucose uptake.

• 5.

  5. In the presence of insulin (0.1 I.U./ml), the addition of ouabain gave a further stimulation of glycogen synthesis. This was accompanied by a decrease in lactate production and a slight depression of the glucose uptake.

• 6.

  6. Furthermore, it was shown that ouabain in concentrations down to 1.4·10⁻⁶ M induced an inhibition of CO₂ production from glucose.

From a study of proteins containing cystine residues, it is concluded that during high-energy irradiation electrons are trapped on the cystine residues. The resultant cystine anion reacts to give the -CH₂S^• radical previously observed by other workers. These reactions are affected by freeze-drying the proteins from solutions of different pH's and can be prevented by additives which scavenge electrons. If the protein contains cysteine residues, -CH₂S^• radicals are formed also by the migration of radicals on to the sulphydryl group of the cysteine. These results have been supported by a study of the radical reactions in irradiated oxidised and reduced glutathione.

The accelerating effect of leucine on the transintestinal transport of lysine has been studied.

The relationship of the transport of lysine to that of leucine was such as would be expected if the accelerating effect of leucine was a result of the combined function of the transport mechanisms of the neutral and the diamino acids. Of the two transport mechanisms that of the neutral amino acids created and maintained, on the serosal side of the transport mechanisms, a concentration of leucine sufficient to exert a counterflow effect on the transport of lysine by the transport mechanism of the diamino acids.

The transintestinal transport of arginine and ornithine was accelerated by leucine to the same extent as that of lysine.

A soluble cytochrome oxidase preparation was obtained from the particulate preparation of dark-aerobically grown Rhodopseudomonas spheroides cells by treatment with non-ionic detergent. The preparation contained appreciable amounts of a- and c-type cytochromes and a small amount of b-type cytochrome. The oxidase preparation displayed the typical features of a cytochrome oxidase in reactivity. No evidence could be obtained for the occurrence of an o-type of cytochrome in dark-grown Rps. spheroides. The oxidation-reduction potential of the soluble Rps. spheroides cytochrome 550 was found to be +0.34 V, whereas that of the particle-bound c-type cytochrome was approx. +0.25 V.

It was concluded that the physiological terminal oxidase of dark-grown Rps. spheroides is the a-type cytochrome, and that particle-bound c-type cytochrome is the physiological electron carrier for it.