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

• 1.

  1. The chlorophylls and the corresponding phaeophytins of 18 species of photosynthetic bacteria have been characterized by paper chromatography and by absorption spectra in visible light.

• 2.

  2. Except for one species of Rhodopseudomonas which contained bacteriochlorophyll b, all the Thiorhodaceae (four) and the Athiorhodaceae (nine) species investigated as well as Rhodomicrobium vannielii had bacteriochlorophyll a as the only detectable chlorophyll.

• 3.

  3. The chlorophyll-770 of Chlorobacteriaceae (four strains or species) was found to be spectroscopically and chromatographically identical with bacteriochlorophyll a.

• 4.

  4. The chlorobium chlorophylls-650 and -660 were each separated by paper chromatography into three fractions. In the case of chlorobium chlorophyll-650 two of the fractions each gave rise to one phaeophytin, whereas the last fraction gave three phaeophytins. All phaeophytins had identical absorption spectra, but exhibited different R_F-values on paper chromatograms.

• 5.

  5. In addition to the chlorophylls mentioned above, all the species of the Chlorobacteriaceae contained trace amounts of a hitherto undescribed chlorophyllous pigment.

• 6.

  6. A revision of the current nomenclature for bacterial chlorophyll is proposed.

A membrane fraction isolated from Ehrlich ascites carcinoma microsomes contians an ATP phosphohydrolas which is strongly stimulated by K⁺ in the presence of Na⁺. The enzyme system has an absolute requirement for Na⁺ and Mg²⁺, but a number of monovalent cations can simulate K⁺. Ca²⁺, ADP and ouabain are inhibitory. The enzyme is believed to be associated with plasma membrane fragments.

The quantitative relationships between enzyme activity and reactant concentration is presented and the probable relationship between ion transport in the whole cell and the alkali-cation-sensitive ATP phosphohydrolase is discussed.

Pulsed electric fields were applied to F-actin oriented by flow and the process of dis- orientation was followed by birefringence measurements. An electric field parallel to the filament axis of F-actin produced a large disorientation effect whereas a perpendicular field produced a small effect. The analysis of the birefringence decrease in normal and reversed pulses at various field strengths suggests that F-actin has a large permanent dipole moment perpendicular to the filament axis. The marked disorientation effect of the parallel field on F-actin vanished on addition of H-meromyosin. On dissociation of the complex of F-actin and H-meromyosin by the addition of ATP the disorientation effect of the parallel field was again observed. This result suggests that a strong electric interaction exists between (permanent) dipoles of F-actin and H-meromyosin.

A small particle fraction has been prepared from Chromatium which reduces NAD by both photo and dark reactions. The reductions are stimulated by the addition of two Chromatium enzymes, a flavoprotein and cyrstalline ferredoxin.

Irradiating a solution of thymidyl-(5′-3′)-bromodeoxyuridine with monochromatic, ultraviolet light yields one main photo-product, an intramolecular dimer, containing no Br and a cyclobutene ring structure. In the presence of cysteine and ultraviolet radiation the dimer is further decomposed to a photo-product characterized by an end-absorption spectrum. This compound contains one S atom per dinucleotide and cannot be reverted by irradiation at 2400 Å. The quantum yields of this sulfhydryl addition are measured as a function of wavelength. The reaction kinetics and the biological implication of this process, which is possibly radio-protective, are discussed.

Volume changes in glycerol-extracted myofibrils were studied. The effect of pH, ion content and ATP concentration on the change in volume was determined. A volume change greater than that attributed to ATP dephosphorylation was observed. The magnitude of the volume change of the entire system was 10⁻³ cm³ whereas that due to dephosphorylation was 10⁻⁶ cm³. The ratio of ATPase activity in a volume decrease to that in a volume increase was found to be approx. 10:1. The total amount of volume decrease measured approx. 0.028 cm³/g of muscle with a fresh myo fibril preparation. The volume increase which was observed upon the addition of large amounts of ATP amounted to approx. 0.036 cm³/g of muscle. The relationship between the volume changes and molecular reorganization of the myofibril proteins was discussed. It was concluded that either a large configurational change occurs in the myofibril proteins during an ATP-induced contraction or relaxation, or that the volume changes are related to the dissociation and association of actin and myosin filaments