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

• 1.

  1. Absorption spectra of various species of purple bacteria at 20° and −170° with a high spectral resolution, and spectra of light-induced absorbance changes, occurring upon illumination with light of a relatively low intensity, were measured in the near-infrared wavelength region between 750 and 950 mμ.

• 2.

  2. At least 5 spectroscopically different bacteriochlorophyll types, namely B^∗800, B 800, B 820, B 850 and B 890, were observed in Chromatium B^∗800, for which the maximum of the absorption band is at a somewhat lower wavelength than that for B 800, was also found in the Thiorhodaceae Rhodothece conspicua and Thiocapsa floridana; B 820 was also found in Rh. conspicua and in Rhodopseudomonas palustri. All species examined, except Rhodospirilium rubrum, contained B 850 in addition to B 890.

• 3.

  3. In all species, except R. rubrum and Rps. palustris, the absorption bands of either B 820 or B 850 and of B 890 shifted upon illumination towards a slightly longer wavelength. An analysis of the B 850 shift in Rhodopseudomonas spheroides indicated that allumination causes a shift of about 1.25 ± 0.20 mμ and that 25–28% of the B 850 molecules participate in this reaction. It was estimated that in this species the absorption bands of 10–15 molecules of B 850 were shifted per light quantum absorbed at 593 mμ. In Th. floridana and Rth. conspicua there occurred in addition a shift of a band at about 800 mμ towards a shorter wavelength. Lowering of the temperature also effected a shift of the bands of B 820, B 850 and B 890 towards a longer wavelength.

• 4.

  4. The light-induced spectral shifts are interpreted as being caused by conformational changes in the carrier molecules of the bacteriochlorophyll types.

A suspension of Chlorella was illuminated long enough for the induction period to be complete and thus for stead-state photosynthesis to be achieved. Then the exciting light was chopped by a slotter about 4 times per sec and the capacity of the algae to fluoresce was followed by means of a low-intensity measuring beam during the dark period. The decay of the fluorescence capacity was approximately exponential and was characterized by a time constant of about 20 msec at room temperature. The temperature dependence of this time constant fits an Arrhenius equation with an activation energy of 0.34 eV. We concluded from these results that fluorescence provides a direct measure of photosynthetic energy migration during steady-state photosynthesis and also that the kinetically limiting step in this energy migration involves the electron transport chain enzymes.

The transport of sodium through the marine algae Ulva lobata and Ulva expansa has been studied by a tracer analytical method. Sodium was transported across Ulva at a rate of 0.15% per min in the dark; this rate was slowed by ouabain and increased by formaldehyde. Dinitrophenol, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and ammonium ion had no effect on the dark rate. Light caused a transient, rapid light extrusion of sodium from the algae equal to approximately twice the amount of sodium expected during a two minute dark period. All the inhibitors adversely affected the efflux of sodium due to light. Comparison of the ability of choline and sucrose to elute sodium from Ulva showed that a high portion of the sodium can be released, but only by a process similar to ion exchange.

The kinetics of potassium exchange in cells of Staphylococcus aureus with ⁴²K⁺ as a tracer in the extracellular potassium phase, was investigated. In phosphate buffer and KCl, in the absence of glucose, results showed that equilibration of distribution of external specific radioactivity and internal specific radioactivity was not achieved because the cells continuously lose potassium. In the presence of glucose, however, results showed no loss of potassium from the cells, and the potassium phase in the cells remained stationary, so that an equilibrium between intracellular and extracellular specific radioactivity was achieved. Sodium azide and dinitrophenol, added in both the absence and presence of glucose, did not have any effect on exchange as compared with controls. If, however, DL-glyceraldehyde was added in the experiments in the presence of glucose, no utilization of the carbon source, and the same behaviour for the cells as in the absence of glucose, was observed. Incubation temperature has a marked effect: potassium-exchange rate is greatly decreased at a temperature of 4°. Increasing concentrations of potassium in the suspension medium did not affect the exchange rate for concentrations higher than 3–4 mequiv potassium per 1.

A precise and sensitive integrating spectrophotometer has been constructed in the shape of a dodecahedron with one photoelectric cell on each side. With the help of this instrument and a computer, the red chlorophyll $\text{a}$ absorption band of algae and chloroplasts was resolved (after subtracting the chlorophyll $\text{b}$ band) into two Gaussian components, with peaks at 668 and 683 nm^★★. The half-width of the two-band envelope is 32 nm; the half-width of each component, about 18 nm. In the blue-green alga, Anacystis and the red alga, Porphyridium (both containing no chlorophyll $\text{b}$), the two-component bands seem to be in the same positions, but are considerably wider. (However, preliminary analysis suggests that the red band in Anacystis can be interpreted instead as the sum of three components—two belonging to chlorophyll $\text{a}$, and a third one probably due to allophycocyanin.) The relative heights of the two chlorophyll $\text{a}$ components vary, in all plants used, only between 0.7 and 0.9, the 668-nm band always being the weaker one.

Broadening of chlorophyll $\text{a}$ absorption curves by the so-called “sieve effect” may to some extent change the analysis presented here, by causing the component bands in vivo to deviate from the Gaussian shape; this effect calls for further investigation but is unlikely to affect the qualitative conclusions.

A comparison of the absorption spectrum so analyzed with that of the “Pigment systems I and II” (Duysens, Frenchet al.) suggests that in Chlorella, a large portion of chlorophyll $\text{a}$ 668 nm belongs, together with a large part of chlorophyll $\text{b}$, to System II, while a large part of chlorophyll $\text{a}$ 683 nm must be identified with System I, although some of it probably belongs to System II. The simple identification of chlorophyll $\text{a}$ 668 nm with System II, and chlorophyll $\text{a}$ 683 nm with System I, as previously suggested, appears to be untenable. In red and blue-green algae, larger parts of both chlorophyll $\text{a}$ 668 nm and chlorophyll $\text{a}$ 683 nm seem to belong to System I.

• 1.

  1. A method is described by which corticosterone was directly extracted from rat adrenal glands under an applied electrical field in the middle chamber of a seven-compartment electrodialysis-type apparatus. Anion- and cation-permeable membranes were used to separate the chambers which were filled with acetate buffer or water.

• 2.

  2. With the conditions used, whole glands with intact capsules could not be extracted. Good extraction of adrenal corticosterone was obtained when halved adrenal glands were used and when cation-permeable membranes limited the middle or extraction chamber. In this case 95% of the corticosterone was extracted in less than 5 min while little or no corticosterone was extracted from the glands in the absence of cation migration into the middle chamber.

• 3.

  3. Synthesis of corticosterone occurred de novo when a cation-permeable membrane limited the anodic side and an anion-permeable membrane the cathodic side of the extraction chamber.

• 4.

  4. The amount of corticosterone extracted depended also on the orientation and position of the adrenal halves in the extracting chamber.

• 5.

  5. The rapid and almost complete extraction of corticosterone with an electrical current suggests the movement of a charged corticosterone complex.

• 1.

  1. The intestinal absorption of L-phenylalanine, determined by measuring the accumulation of the labelled amino acid in the tissue during an incubation in vitro, shows an absolute dependence on the presence of sodium ions in the incubation medium. In the absence of these ions, there exists a barrier against the penetration of the amino acid into the mucosal cells. During gradual ageing of the tissue in vitro, the loss of efficiency of this barrier is coincident with the loss in capacity to transport the amino acid against a concentration gradient.

• 2.

  2. The accumulation of L-phenylalanine by a fragment of intestine is dependent on, but is not directly proportional to, the sodium ion concentration of the incubation medium.

• 3.

  3. After preincubation in a sodium-free medium, a tissue sample is no longer capable of transporting L-phenylalanine against a concentration gradient; the findings resemble those following preincubation under anaerobic conditions. Nevertheless, the tissue continues to respire normally and to maintain the barrier against non-specific entry into the mucosal cells in the absence of these ions. Furthermore, perfusion of a loop of rat intestine in vivo with a sodium-free buffer solution has no deleterious effect on its subsequent ability to absorb L-phenylalanine in vitro. These apparently contradictory results are discussed in the light of the most modern theories of intestinal transport of non-electrolytes.

• 4.

  4. The exit of labelled L-phenylalanine from a tissue previously saturated with this substrate may be stimulated by the presence of the unlabelled amino acid in the surrounding medium. This mechanism is also dependent on the presence of sodium ions in the solution. The full interpretation of these results must wait until it has been shown in which membrane of the cell this exchange mechanism takes place.

High activities of transport ATPase and diglyceride kinase, relative to other preparations, were observed in a deoxycholate-treated particulate fraction from guinea-pig cerebrum. Incubation of the enzyme preparation in various buffers showed an initial inactivation of the diglyceride kinase and a slight activation of the transport ATPase. Both enzymes were irreversibly inhibited on treatment with DFP. In the presence of strophanthidin both enzymes showed similar but not identical rates of inhibition by DFP. The effects of DFP concentration and pH on the inhibitions of both enzymes were similar. ATP protected both enzymes against DFP inactivation, but very much lower concentrations were required for protection of the transport ATPase. Mg²⁺ was required for DFP inhibition of transport ATPase but not of diglyceride kinase, even though the latter could be shown to require Mg²⁺ for activity. Strophanthidin or K⁺ potentiated the inhibitory effects of DFP on transport ATPase but had no effect on the inhibition of diglyceride kinase. The brain enzyme preparation also contained phosvitin kinase. It was slightly inhibited by DFP during the first few minutes of incubation; no further inhibition was observed on longer incubation. Removal of a sulfhydryl inhibitor from the DFP preparation by fractional distillation did not reduce the inhibitory effect of DFP on the three enzymes. Under conditions in which the rate of inhibition of the transport ATPase by DFP was increased 2.5-fold by strophanthidin there was no increased phosphorylation of the enzyme preparation by [³²P]DFP. The possibility that the transport ATPase is a modified form diglyceride kinase, in which water has become the favored phosphate acceptor, is discussed. Tetraethylpyrophosphate showed about the same potency as DFP in inhibiting the transport ATPase.

Adenosine and inosine are rapidly taken up by suspensions of Escherichia coli by transport processes that can be differentiated from the slower subsequent formation of phosphorylated intermediates. The uptake mechanisms are saturable, are inhibited by heavy metal ions and energy poisons, and show a high temperature coefficient near 0°. Inosine efflux is also markedly temperature dependent and is inhibited by heavy metal ions. Efflux of inosine is increased by the influx of other nucleosides. Other nucleosides lower the rates of adenosine and inosine entry but free bases show little inhibition. Caffeine retards the rates of inosine influx and efflux but does not effect the adenosine uptake mechanism.

Transport can also be measured by the rate of deamination of adenosine by intact cells. Comparison of the similarities and differences for isotope uptake, release, and cellular deamination leads to the conclusion that adenosine and inosine are transported across the cell membrane by processes that are separate, but overlapping, and which have a facultative requirement for metabolic energy.