The back reaction in the primary electron transfer couple of photosystem II of photosynthesis

Changes of C-550, cytochrome b₅₅₉ and fluorescence yield induced in chloroplasts by single saturating flashes were studied at low temperature. A single saturating flash at −196°C was quite ineffective in reducing C-550, oxidizing cytochrome b₅₅₉ or increasing the fluorescence yield, presumably because most of the charge separation induced by the flash was dissipated by a direct back reaction in the primary electron transfer couple. The back reaction, which competes with the dark reduction of the oxidized primary electron donor by a secondary electron donor, becomes increasingly important as the temperature is lowered because of the temperature coefficient of the reaction with the secondary donor. The effect of the back reaction is to lower the quantum yield for the production of stable photochemical products by steady irradiation. Assuming a quantum yield of unity for the photoreduction of C-550 at room temperature, the quantum yield for the reaction is about 0.40 at −100°C and 0.27 at −196°C.     

Coumarins and chromones from Lomatium macrocarpum

Roots of Lomatium macrocarpum (Hook. & Arn.) C. & R. yielded osthol (7-methoxy-8-[3-methyl-2-butenyl]-coumarin) and a chromone, 2-methyl-5-hydroxy-6-[3-methyl-2-butenyl]-7-methoxychromone, identified spectroscopically and by synthesis. The aerial parts of the plant also contained this chromone along with sibiricin (5,7-dimethoxy-8-[3-methyl-2,3-epoxybutyl]-coumarin) and a new coumarin named macrocarpin. By spectroscopy and chemical degradation macrocarpin was shown to be 7-methoxy-8-(3-methyl-4-[2-methyl-cis-2-butenoyloxy]-cis-2-butenyl)coumarin. These products were not found in four other Lomatium species examined.     

The relationship of serine protease activity to RNA polymerase modification and sporulation in Bacillus subtilis

The isolation and properties of a single site temperature sensitive protease mutant of Bacillus subtilis are described. Numerous criteria suggest that the mutation resides in the structural gene coding for a basic serine protease. The mutation has been mapped between aroD and lys-1 on the Bacillus subtilis chromosome. This protease exists as an intracellular and extracellular enzyme. The mutant cells are temperature sensitive for sporulation, antibiotic production, and the sporulation-specific alteration in DNA-dependent RNA polymerase β subunit. Several types of evidence indicate a direct involvement of this enzyme in a limited proteolytic cleavage of vegetative RNA polymerase β subunit, which produces the lower molecular weight β subunit found in sporulating cells. The derangement in this process is sufficient to account for the stoppage of sporulation at stage 0 when the mutant cells are grown at the non-permissive temperature.     

Studies on the Biosynthesis of α-Putrescinylthymine in Bacteriophage φW-14-Infected Pseudomonas acidovorans

The alpha-putrescinylthymine (putThy) in bacteriophage phiW-14 DNA is synthesized at the mononucleotide level: it is labeled by uracil or deoxyuridine but not by thymidine, and it appears in the acid-soluble pool of infected cells before the onset of phage DNA synthesis. The methylene group at the C-5 position of the pyrimidine moiety of putThy is derived in vivo from a C(1) unit. Extracts of a phage infected thymidine auxotroph of the host, Pseudomonas acidovorans, apparently contain a phage-specific thymidylate synthetase and a phage-specific activity which forms 5-hydroxymethyl dUMP from N(5), N(10)-methylene-tetrahydrofolate and dUMP.     

Enrichment Procedure for Use with the Membrane Filter for the Isolation and Enumeration of Fecal Streptococci in Water

By the use of PYC enrichment medium, the recovery of fecal streptococci from river water has been increased more than twofold over that of M-Enterococcus Agar. Of the isolates tested, 94.6% could be classified as enterococci or enterococcus biotypes. This method seems to yield a larger number of strains which would not normally be revealed. Serological typing of atypical streptococcus strains isolated indicates that the majority of these “biotypes” can be placed in the enterococcus group.     

A REVIEW OF THE LITERATURE ON THE ETIOLOGY OF HODGKIN'S DISEASE

Extensive research to trace the cause of Hodgkin''s disease to a bacterial or protozoan agent has proven fruitless.Although a viral cause for Hodgkin''s disease has been previously suggested, early explorations along that line have not been confirmed. With the development of newer techniques for the study of viral characteristics certain apparently significant factors in Hodgkin''s disease have been encountered. Most promising has been the consistent demonstration that Seitz-filtered, sterile Hodgkin''s disease lymph node extract can be passed serially in fertile chicken eggs and that the amniotic fluid from these eggs possesses the capacity to interfere with the growth of influenza virus in eggs.     

Thermal Destruction Kinetics of a Lactic Streptococcal Bacteriophage

The aim of the study was to elucidate the kinetics of thermal destruction of a lactic streptococcal bacteriophage, and to determine the effect of varied propagation and heating conditions on its thermoresistance. The propagation medium and temperature affect the degree of thermostability of the phage produced; higher incubation temperature enhances thermostability. The composition and reaction of the heating menstruum are also of significance. Phage thermoresistance increased significantly with the phosphate and whey levels. The effect of various minerals was difficult to resolve, mainly because of the bimodal nature of the survival curve. Thermoresistance was highest at pH 6, intermediate at pH 7, and lowest at pH 8. The kinetics of inactivation of this phage deviated from those of a first-order reaction. Consequently, a special treatment of the data was required in order to compute the various thermodynamic parameters that define the reaction. The high positive values of Q₁₀, energy of inactivation, and entropy appear to indict protein denaturation as the cause of phage destruction.