Effects of DDT on photosynthetic electron flow in Secale species

Following a survey of a range of varieties of rye, mainly Secale cereale, for reaction to DDT, the mode of action of the pesticide in a susceptible variety was studied. Two sites of interaction of DDT with the photosynthetic electron transport chain were demonstrated. The first site of inhibition was on the oxidizing side of photosystem 2, between the sites of electron donation from diphenylcarbazide at pH 6.0 and pH 8.0 in Tris-washed chloroplasts. The second site of DDT inhibition was in the intermediate electron transport chain, and was demonstrated by using dichlorophenol-indophenol and phenyldiamines as electron donors in chloroplasts where electron flow from photosystem 2 was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The sites are distinct from those characteristic of herbicides which affect photosynthetic electron flow.     

Phenazine methosulfate stimulation of ouabain-sensitive Rb+ uptake by HeLa cells: effects of respiratory inhibitors, anaerobiosis, and ascorbate

phenazine methosulfate (PMS) stimulates ouabain-sensitive Rb+ uptake by HeLa cells. This stimulation cannot be attributed to the effect of the dye on the intracellular Na+ or ATP content. Respiratory inhibitors, such as 5 mM NaCN and 5 microM rotenone, and anaerobic conditions enhance the stimulation of Rb+ uptake by PMS. Cellular respiration is stimulated, but lactate production is reduced in the presence of PMS, irrespective of the presence of respiratory inhibitors. Cellular NADH is oxidized markedly on addition of PMS plus inhibitors, but it is not affected by addition of the inhibitors only. In the presence of a high concentration of PMS, PMS-stimulated ouabain-sensitive Rb+ uptake is inhibited by addition of ascorbate. From these results it is concluded that Na+K-pump activity is closely related to the cellular redox state.     

The characterisation of inducible dehydrogenases specific for the oxidation of d-alanine,allohydroxy-d-proline,choline and sarcosine as peripheral membrane proteins in Pseudomonas aeruginosa

The interaction with the cytoplasmic membrane of the inducible, membrane-bound, cytochrome-linked dehydrogenases specific for the oxidation of d-alanine, allohydroxy-d-proline, choline and sarcosine in Pseudomonas aeruginosa was investigated. The susceptibility of d-alanine dehydrogenase to solubilisation by cation depletion or by washing with high ionic strength buffers indicated that it was a peripheral membrane protein. The effect of various divalent cations in reducing the amount of enzyme released by cation depletion suggests a requirement for Mg²⁺ in the binding of d-alanine dehydrogenase to the cytoplasmic membrane. The peripheral nature of all four dehydrogenases was confirmed by examination of the molecular properties and phospholipid content of preparations of the enzymes solubilised with 1 M phosphate buffer (pH 7.0). Additional confirmatory evidence was provided by Arrhenius plots of membrane-bound activity of d-alanine and allohydroxy-d-proline dehydrogenases which were monophasic and independent of the discontinuities attributable to membrane lipid phase separations which characterise such plots of the activity of integral membrane-bound enzymes. The shape of the Arrhenius plots obtained for the activities of known integral respiratory proteins of P. aeruginosa suggests that these enzymes may remain in a fluid environment throughout the course of the phase separation.     

Ca2+ and calmodulin antagonists inhibit the proton gradients associated with non-cyclic and cyclic photophosphorylation in spinach chloroplasts

The synthesis of benzylpenicillin (BP) after mixing phenyl-acetyl-glycine(PAG), 6-aminopenicillanic acid (6-APA) and free or immobilized penicillin amidase (E.C.3.5.1.11.) was studied as a function of pH and ionic strength. Before the final equilibrium was reached a kinetically controlled synthesis of BP was observed. Then a transient maximum concentration in BP much larger than the final equilibrium content was synthesized in the acyl-transfer process. The factors influencing this maximum have been analyzed. Increasing ionic strength markedly decreased the maximum in BP and the rate of deacylation of phenyl-acetyl-penicillin amidase by 6-APA. The change was largest when the enzyme was immobilized in a positively charged support, where at low ionic strength the concentration of 6-APA around the enzyme is larger than the bulk concentration due to the partitioning of charged solutes.     

Schistosoma mansoni: Electrophoretic characterization of strains selected for different levels of infectivity to snails

Individual adult Schistosoma mansoni from strains selected for high or low infectivity to specific strains of the snail intermediate host, Biomphalaria glabrata, were subjected to enzyme electrophoresis on starch gels. Fourteen enzyme systems were analyzed in an attempt to find electrophoretic markers associated with genes for infectivity to snails. The S. mansoni strains were selected from different isolates from Puerto Rico in several strains of B. glabrata. Of an estimated 18 loci, 3 were polymorphic and the remainder monomorphic. For 1 of the 3 polymorphic enzyme loci, lactate dehydrogenase (Ldh, EC 1.1.1.27), phenotype frequencies were correlated with infectivity to snails. In schistosome strains of low infectivity, frequencies of the Ldh-N phenotype ranged between 0.56 and 0.69, while in strains of high infectivity, Ldh-N frequencies were typically 0.91 to 1.00. Whether the correlation is accidental or due to some form of association, such as chromosomal linkage, between the locus responsible for variation in lactate dehydrogenase and a gene for infectivity to snails remains to be determined.