In vitro effects of DDT analogs on trout brain Mg2+-ATPases: Inhibition kinetics

A continuous in vitro steady-state assay procedure was used to investigate the dependence of trout brain mitochondrial Mg²⁺-stimulated adenosinetriphosphatase specific activity on temperature and substrate concentration. The inhibition of enzyme activity by DDT was independent of substrate concentration. DDT and several analogs caused increases in the experimental activation energy and frequency factor of the enzyme-catalyzed reaction, which gave rise to a negative temperature coefficient of inhibition. It is suggested that DDT and other highly lipophilic compounds have the potential to allosterically affect membrane-bound enzymes by simply becoming a major lipoid component of the membranes.     

A study of liver function in rats with mirex-induced enlarged livers

The functional capacity of a mirex-induced, enlarged liver was studied in rats. The tests used were sulfobromophthalein clearance, hepatic cytochrome P-450 concentration, serum total protein concentration and electrophoretic pattern, serum total lipid concentration, serum glucose concentration, and the liver response to epinephrine. There was no indication of a loss of functional capacity in the enlarged liver. Sulfobromophthalein clearance and microsomal cytochrome P-450 concentration indicated an increase in total liver functional capacity. We conclude that mirex is not a direct hepatotoxin producing generalized parenchymal cell damage.     

Effect of tricyclazole on growth and secondary metabolism in Pyricularia oryzae

Tricyclazole [5-methyl-1,2,4-triazolo (3,4-b)-benzothiazole] controls rice blast disease caused by Pyricularia oryzae at concentrations (5–10 μg/ml) which do not inhibit growth of the pathogen in vitro. However, concentrations of 1 μg/ml or less inhibit melanin formation in the fungus. Production of pyriculol by the pathogen is usually enhanced by 10 μg/ml of tricyclazole, whereas production of 3,4-dihydro-4,8-dihydroxy-1(2H)-naphthalenone is strongly inhibited or markedly reduced and delayed. Evidence suggests that tricyclazole blocks aspects of polyketide metabolism in P. oryzae which may have a role in pathogenicity.     

Inhibition of chitin synthesis by two 1-(2,6-disubstituted benzoyl)-3-phenylurea insecticides. II

The knowledge of the biochemical mode of action of 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea (diflubenzuron) is presented, explaining the insecticidal effect. Like its structural analog, 1-(2,6-dichlorobenzyl)-3-(3,4-dichlorophenyl)urea (Du 19111), it inhibits chitin synthesis in the cuticle of larvae. Virtually complete inhibition was demonstrable 15 min after the application of diflubenzuron. Neither diflubenzuron nor Du 19111 has any effect upon chitinase activity either in vivo or in vitro. The insecticidal effect upon the cuticle, therefore, must be explained as an inhibition of chitin synthesis and not as an activation of chitin degradation. In contrast to the action of Du 19111, no accumulation of N-acetylglucosamine occurs upon treatment of larvae with diflubenzuron. Similarities and differences in the mode of action of both compounds are discussed, together with other effects reported in the literature.     

Ultrastructural changes in leaf and needle segments treated with herbicides containing picloram

The herbicide Tordon 50D (picloram+2,4-D) affected the integrity of the nucleus and cell membranes in Pinus radiata needle segments and caused the swelling of internal chloro plast membranes and the eventual disintegration of the chloroplasts. Tordon 22K (picloram) only affected chloro plast structure. Both herbicides had similar adverse effects on cell membranes and chloroplasts of Eucalyptus viminalis.     

The selectivity of methabenzthiazuron between barley, perennial ryegrass and Poa trivialis

In field experiments methabenzthiazuron at 1.1 kg ai/ha applied pre-emergence gave good control of Poa trivialis L. in perennial ryegrass S23 which was undersown in spring barley (Zephyr); no significant damage to barley or perennial ryegrass resulted from 2.2 kg ai/ha. However this dose applied when barley had three to four leaves decreased the subsequent barley yield. In pot experiments in the glasshouse methabenzthiazuron was active mainly due to uptake through the soil. Much greater damage to barley and perennial ryegrass resulted when herbicide-treated soil was placed below seed level than above the seed. The difference was less marked with P. trivialis. The latter started to develop secondary roots near the soil surface earlier than either perennial ryegrass or spring barley.     

Structure-activity relationships of 1,2,3-benzothiadiazoles as synergists for carbaryl against the house fly (Musca domestica)

Fifty six 1,2,3-benzothiadiazoles and related compounds were evaluated as carbaryl synergists against the house fly (Musca domestica). Many of these were excellent synergists, the most active being those containing various combinations of halogen, alkyl, or alkoxy substituents in the 5- and/or 6-positions of the ring.Regression analysis on the data from 14 compounds for which substituents constants were available established that synergistic activity can be satisfactorily described by equations in terms of the hydrophobic bonding constant (π) and the homolytic free radical constant (σ ·).The results with compounds related to the 1,2,3-benzothiadiazoles suggest that synergistic activity is associated primarily with the diazosulfide moiety.     

Studies on viremia and antibody formation in ducklings and goslings after experimental infection with Lednice (Yaba 1) virus.

A very low virus level was found for a short time in the blood of ducklings and goslings after experimental Lednice (Yaba 1) virus infection by subcutaneous (scut) and intranasal (inas) route and in blood of ducklings also after infection by intracerebral (icer) route. Subsequently virus neutralizing antibody formation was examined. Antibody formation was found in most of animals. In goslings onset of antibody formation seems to be slower than in ducklings after the same virus infection dose; vice versa, in ducklings antibody titer decreased after 6 weeks. Using low infection virus dose, neutralizing antibody level in ducklings was lower than in the former case. On examining the blood and the organs, the virus was detected in a very low amount and for a very short time in blood and spleen of goslings and only in blood of ducklings.     

Seasonal activity of EPTC for Cyperus rotundus L. control in a tropical climate*

Four experiments were conducted at six week intervals to determine the seasonal activity and persistence of soil-incorporated EPTC (5-ethyl N,N-dipropyl(thiocarbamate)) for Cyperus rotundus L. control and tolerance of okra (Hibiscus esculentus L.), cucumber (Cucumis sativus L.), lettuce (Lactuca sativa L.), red beet (Beta vulgaris L.) and carrot (Daucus carota L.) during the dry and wet seasons in Viçosa, Brazil. Satisfactory control of C. rotundus was obtained at 2 kg/ha EPTC during the dry season and 4 kg/ha or more during the wet season. Only red beet and carrot tolerated these doses of EPTC when the crops were planted five days after application. However, selective control of C. rotundus was obtained when the planting date of lettuce was delayed for three or six weeks after EPTC application. EPTC controlled C. rotundus at half the dose that was required to control three species of annual grass that germinated near the soil surface. EPTC persisted longer when applied to air dry soil and incorporated with a rototiller than when incorporated into moist or wet soil.     

Dissociation and phosphorylation constants for the inhibition of acetylcholinesterase by a series of novel O-ethyl O-phenyl S-n-propyl phosphorothioates

The phosphorylation, dissociation, and bimolecular reaction constants were determined for several members of a series of substituted O-ethyl O-phenyl S-n-propyl phosphorothioates in the presence of substrate. The data obtained are discussed in relation to electronegativity of substituents and in vivo toxicity.