Biochimica et Biophysica Acta (BBA) - Specialized Section on Biophysical Subjects最新文献

It has been found that: the dark electron-spin-resonance spectrum of spinach chloroplast fragments is reduced in the presence of spinach phosphodoxin; the light-induced electron-spin-resonance spectrum of spinach chloroplast fragments is increased in the presence of spinach phosphodoxin; and spinach phosphodoxin alone exhibits a pH-dependent, light-induced spin signal.

• 1.

  1. During the bioluminescent reaction of the sea pansy, Renilla reniformis, an activated intermediate had previously been described which forms upon incubating Renilla luciferin, Ado-3′-5′-P₂, Ca²⁺, and Renilla lucidferase under anaerobic conditions. A chemically identical intermediate can be formed in the absence of Ado-3′-5′-P₂ and luciferase by treating luciferin at pH 1.0 for 2 min at 100°, during which time a quantitative conversion to the intermediate occurs as judged by total light measurements. Once the intermediate is formed it can be oxidized rapidly by O₂ or H₂O₂, in the absence of luciferase, via a non-luminescent pathway.

• 2.

  2. Since a relatively slow conversion of luciferin to the activated intermediate occurs at high pH at 100° or at pH 7.0 at 130° the suggestion is made that the mechanism of the Ado-3′,5′-P₂-dependent activation of Renilla luciferin involves the cleavage of an unidentified group from the luciferin molecule.

• 1.

  1. The influence of ionic strength, dioxane, and ethylene glycol on the acid transition of ribonuclease has been studied by difference spectrophotometry. In this transition two of the three buried tyrosyl residues of the molecule can be normalized if the temperature is high enough, but an increase in the ionic strength will repress the normalization of one of them. Dioxane makes the normalization of the second one easier, and ethylene glycol has very little effect.

• 2.

  2. Dioxane also raises the pK of the transition. Ribonuclease, serum albumin, and acetic acid all show the same dependence of Δ pK on dioxane concentration, suggesting that the increase is caused by a change in the bulk dielectric constant of the medium. Chymotrypsinogen is much more strongly affected, and lysozyme is less strongly affected.

• 3.

  3. The denaturation of ribonuclease at pH 2.3 by dioxane shows some very unusual features. The difference spectra are anomalous. The denaturation is very strongly affected by the ionic strength, and in an opposite direction to what is usually observed: denaturation occurs at lower dioxane concentrations as the ionic strength is raised. A possible explanation for these unusual features is based on Weber's observation that dioxane first denatures ribonuclease, and at higher concentrations promotes the formation of helical regions in the molecule.

• 1.

  1. Examination of fractions of the main organ of Electrophorus indicates in the “proteinase preparation” an oxidation-reduction system containing cytochromes a₃, a, c₁, c and b. The b component is anomalous in that its antimycin response shows a double band.

• 2.

  2. The “blendor preparation” reveals small amounts of the above cytochromes in the presence of larger amounts of electron-transfer pigments which cannot be identified with known cytochromes.

• 3.

  3. The capability for electron transfer in the organ is small when the calculated rate of oxidative phosphorylation is compared with the rate of glycolysis. It is found that glycolysis can produce ATP at about 90 times the rate as could oxidative phosphorylation in the electric tissue.

• 4.

  4. These data are consistent with the inhibitor insensitivity of the electric discharge of the main organ to anoxia and terminal respiratory inhibitors and confirm the view that glycolytic energy sources are employed in maintaining ionic gradients in the main organ of Electrophorus.

• 1.

  1. The tranquilizing drug chlorpromazine was enxymically oxidized to the freeradical intermadiate which was identical with the red intermediate observed optically at 530 mμ.

• 2.

  2. The stiochiometry for the peroxidaseH₂O₂ reaction was detemrined to be

• 3.

  3. The dismutation reaction rate constant, k_d, at pH 4.8 was measured to be 15.0 M⁻¹·sec⁻. This extreme stability of the free radical allowed further oxidation of the free radical by the enzyme in the substrate-limited case; the rate constant for this reaction was found to be 3.9·10⁻¹, approx. 10 times slower than k₄, the first oxidation.

• 4.

  4. It is suggested that the stability of the free radical may be responsible for the psychotropic activity of the drug.