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

The luminiscence properties of tryptophan chromophores in muramidase are affected by changes in enzyme conformation.

Fluorimetric measurements indicated that the emission spectrum of native muramidase (λ_max. = 337 mμ) was shifted toward longer wavelengths (λ_max. = 350 mμ) as a result of structural changes produced by disruption and carboxymethylation of disulfide bonds. When the disulfide bonds were reformed at pH 8, the emission spectra of reoxidized muramidase resemble that of native muramidase with regard to both general structure and band position.

The phosphorescence spectra of the muramidase species revealed the predominant contribution of tryptophan chromophores to the long-lived emission, and this observation was substantiated by decay-time measurements.

The τ_p values of native and reoxidized muramidases (τ_p = 1−1.9 sec) were remarkably shorter than the τ_p value of reduced carboxymethylated muramidase (τ_p = 4.1 sec). The possible significance of these phosphorescence and fluorescence studies are discussed.

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.

• 1.

  1. The metabolism of ¹⁴C-labelled glycollate and glycine both to sucrose and to a polyglucan via serine has been demonstrated in excised pea leaves. The effect of light, DCMU, isonicotinyl hydrazide and the partial pressure of CO₂ on the pathway has been studied.

• 2.

  2. The metabolism of [¹⁴C]glycine and serine formed during a preceding period of photosynthesis has been followed during a subsequent period of photosynthesis in ¹²CO₂. The radioactivity in the glycine and serine declined whilst that in sucrose rose, suggesting that in photosynthesis some sucrose is formed via glycine and serine. The effect of changes in partial pressure of carbon dioxide indicates that the photosynthetic pathway may be spatially separated from that which metabolises exogenous glycine and glycollate.