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

A kinetic method is described which seems capable of distinguishing between certain rather general types of models for the sodium pump. This analysis is used to compare experimental results with the predictions implied by the models and it is shown that some models are unsatisfactory.

The binding of β-actinin, the actin-dispersing factor, to F-actin has been investigated. The stoichiometric ratios for the binding of β-actinin to F-actin were found to be 1:10 and 1:8, by weight, for intact and sonicated F-actin, respectively.

When an increasing amount of β-actinin was added to F-actin and subjected to sonication, F-actin could be dispersed into particles as short as 3000–4000 Å. Such short F-actin particles were also formed when G-actin was polymerized in the presence of a large amount of β-actinin.

Experimental conditions were checked for the action of β-actinin on the apparent particle length of F-actin. β-Actinin was found to become slowly inactivated in 0.1 M KCl.

• 1.

  1. Streptococcus fecalis maintains an intracellular K⁺ concentration of 559 mM and an intracellular Na⁺ concentration of less than 5 mM when growing exponentially in a medium containing 4.6 mM K⁺ and 151 mM Na⁺. Cells harvested from the stationary phase are K⁺-poor and Na⁺-rich.

• 2.

  2. An energy-dependent net uptake of K⁺ is observed following resuspension of K⁺-poor, Na⁺-rich cells in a neutral medium containing both substrate and K⁺.

• 3.

  3. Net K⁺ uptake under these conditions is the result of two cation-exchange processes: (i) a K⁺−Na⁺ exchange which accounts for aapprox. 60% of the total K⁺ uptake; and, (ii) a K⁺−H⁺ exchange utilizing H⁺ present in the cell at the time of harvesting.

• 4.

  4. Net cation transport is absolutely dependent on the metabolism of exogenous substrate, and both glucose and arginine will support the process, though at significantly different rates. With either substrate, the initial rate of net K⁺ uptake is equal to the calculated rate of ATP production.

• 5.

  5. A transient two-fold increase in the glycolytic rate is closely associated with the onset of K⁺ uptake indicating a coupling between active cation transport and energy-yielding processes in this organism.

During a study of the mechanism of transport of sugars in Nocardia, it was found that sodium arsenate was able to restore the phosphate-requiring glucose uptake.

On examination of the distribution of arsenic in the cells, it was found that the cellular residue obtained after lipid extraction shows only traces of arsenic (1.0 μg/250 mg of cells) as against 15.0 μg of arsenic in the corresponding lipid extract (chloroform-methanol, 2:1, v/v).

After separation of the acetone precipitable and soluble lipids, all the arsenic remains in the polar fraction. This arsenic was not liberated into the water after orientation of the polar lipids in a water-lipid interphase during a period of 18–24 h.

A preliminary identification of the polar lipids of Nocardia by a silicic acid column, paper and thin-layer chromatography shows that the arsenic appears to be associated with at least two different spots with R_F values similar to those of phosphoinositols and sphingomyelin-type compounds.

Arsenic-lipid complex formation as a possible component of a carrier system in sugar transport in Nocardia is discussed.

• 1.

  1. Action spectra for bacteriochlorophyll fluorescence were measured for a number of species of purple bacteria. For a few species action spectra for light-induced absorbance changes (light-induced cytochrome oxidation and shift in carotenoid absorption) were also measured, and were found to be similar to the action spectra for fluorescence.

• 2.

  2. In a number of species, e.g. Chromatium and Rhodopseudomonas spheroides, the action spectra were different from the absorption spectra, indicating that the efficiency of the transfer of excitation energy to the longest-wavelength form of bacteriochlorophyll may be lower than 100% for some types of bacteriochlorophyll. This applied e.g. to the bacteriochlorophyll types absorping at about 800 mμ and 850 mμ in Chromatium and Rps. spheroides, respectively. A possible explanation is that these bacteriochlorophyll types exist in 2 different pools, with different efficiencies of energy transfer to fluorescent B 890.

• 3.

  3. In Rhodopseudomonas palustris light quanta absorbed absorbed at 800 mμ were more active than quanta absorbed at about 890 mμ in exciting bacteriochlorophyll fluorescence. This may be explained by assuming 2 pools of the bacteriochlorophyll type absorbing around 890 mμ, with different fluorescence yields.

• 1.

  1. Fresh slices of salt gland from the herring gull contained approx. 290 mmoles 3⁺ and 350 mmoles Na⁺ per kg dry weight.

• 2.

  2. During incubation at 1° for up to 4 h there was a loss of some 75 mmoles K⁺ per kg dry weight and an equivalent gain of Na⁺; the slices did not swell significantly. The loss of K⁺ was not increased by incubation at 1° in a K⁺-free medium.

• 3.

  3. The rate of ²⁴Na⁺ efflux from the slices and the ability of the slices to maintain their Na⁺ and K⁺ contents during incubation at 25°, were both dependent upon aerobic conditions and the presence of K⁺ (5 mM) in teh medium, and were inhibited by ouabain (0.05 mM).

• 4.

  4. Methacholine (0.33 mM) induced a temporary stimulation of ²⁴Na⁺ efflux. This stimulation was smaller in the presence than in the absence of K⁺ in the medium, but the sum of the effects of K⁺ adn of methacholine in the presence of K⁺ was greater than the effect of methacholine alone in the K⁺-free medium.

• 5.

  5. Methacholine had no significant effect on the Na⁺ and K⁺ contents of the slices, but did cause a decrease in the specific radioactivity of the Na⁺ of the slices at 25°.

• 6.

  6. The results suggest that methacholine and K⁺ both act on salt-gland cells by increasing the permeability to Na⁺ and that, in addition, K⁺ stimulates a mechanism for coupled movements of Na⁺ adn K⁺

The emission and action spectra of fluorescence of photosynthetic pigments, especially of chlorophyll a, were studied in spinach chloroplasts, Anacystis nidulans, Porphyra yeroensis, Porphyridium cruentum and other photosynthesis organisms at −196°, to elucidate the behavior of the pigments in fluorescence and energy transfer. At −196°, in most of the materials used, three emission bands of chlorophyll a were observed at 684 mμ, 695 mμ and 710–735 mμ (designated as F684, F695 and F-1). The emission and action spectra showed that F684 and F695 were excited by the light absorbed by phycobilins or chlorophyll b (pigment system II) and were excited less effectively, or not at all, by the light absorbed by chlorophyll a (pigment system I). F-1 was excited by both wavelenght regions. The light absorbed by pigment system I was more effective for F-1 than for F684 and F695, and the light absorbed by pigment system II was more effective for F684 and F695 than for F-1. A quantum yield of fluorescence as high as 0.75 was obtained in spinach chloroplasts at −196°. At this temperature, F-1 amounted to approx. three-quarters of the total quanta emitted, even upon excitation by 475-mμ light. It was concluded that two forms of chlorophyll a emitting F684 and F695 are contained in pigment system II, while F-1 is involved in pigment system I. Energy is transferred from pigment system II to I, at least at −196°, and presumbly also at physiological temperatures.

The transintestinal transport of tryptophan by everted sacs of the rat smal intestine was studied. It was shown that:

• 1.

  1. The transport of trytophan was enhanced by methionine, leucine and sarcocine;

• 2.

  2. Trytophan was a potent inhibitor of the transport of leucine;

• 3.

  3. The transport of trytophan was inhibited by higher concentrations of methionine;

• 4.

  4. Tryptophan was a potent competitive inhibitor of the transport of lysine;

• 5.

  5. Lysine inhibited the transport of tryptophan when a part of the intestinal capacity for transport of neutral amino acids was occupied by methionine;

• 6.

  6. The effect of increasing the initial mucosal concentrations of tryptophan or lysine, keeping the initial serosal fluids free of amino acids, was to saturate the capacity for transport of these amino acids;

• 7.

  7. The net transport of tryptophan and lysine from the mucosal to the serosal fluids was reduced if these amino acids were initially present in the serosal fluids. It is concluded that:

• 8.

  (i) tryptophan is a substrate for the carrier of the diamino acids as well as for the carrier of the neutral amino acids;

• 9.

  (ii) The enhancement by methionine, leucine and sarcosine of the transintestinal tryptophan transport represents a counterflow effect of these amino acids on the transport of tryptophan by diamino acid carrier;

• 10.

  (iii) The reduction caused to the transport of tryptophan and lysine by their presence in the initial serosal fluids may be explained as a kinetic consequence of the transport of these amino acids by a mobile carrier.