The effect of temperature on bacterial degradation of EDTA in pH-auxostat

The effect of temperature on the maximum specific growth rate and the cell yield was studied during cultivation of two bacterial strains (LPM-4 and Pseudomonas sp. LPM-410) on EDTA under unlimited cell growth conditions in a pH-auxostat. Both strains displayed linear dependence of reciprocal biomass yield against reciprocal specific growth rate, from which the values of rate of substrate expenditure for cell maintenance and the “maximum” yield (i.e., hypothetical yield without cell maintenance processes) were estimated. Analysis of the maximum yield values based on mass–energy balance theory suggested that oxidation of the carboxylic acid side chains of EDTA by a monooxygenase had zero or low energetic efficiency. An Arrhenius equation with different values of Arrhenius parameters within different temperature ranges gave a good fit with the temperature dependence of both growth rate and biomass yield. Specific growth rates of both strains showed a more pronounced temperature dependence than did the cell yields. A possible kinetic mechanism was suggested which might be responsible for the modes of the temperature dependences of specific growth rate and yield that were found. The mechanism is based on a hypothetical key substance governing the metabolic flows, which is formed in a zero-order reaction and destroyed in a first-order reaction, both rate constants depending on temperature according to the Arrhenius law.     

The cellular dynamics of hepatic receptors for alpha 2-macroglobulin.protease complex and for insulin are different

Making freshly isolated rat hepatocytes permeable by 0.4 g/liter digitonin doubled the number of binding sites for alpha 2-macroglobulin.trypsin complex without changing the affinity. Thus, digitonin unmasked a receptor pool, probably of intracellular origin. The total cellular binding capacity was measured in the presence of digitonin, the surface-exposed in its absence. Upon preincubation of the cells at 37 degrees C, the total cellular binding capacity for alpha 2-macroglobulin.trypsin decreased over a 2-h period to 0.26 of the initial value. By contrast, the surface-exposed binding capacity initially increased in response to a preincubation at 37 degrees C, reached after 20 min a peak value 1.74 times that at 0 time, followed by a decrease. Neither the increase in nor the loss of surface-exposed binding capacity was influenced by inhibitors of lysosomal functions, protein synthesis and glycosylation. Colchicine abolished the increase in surface-exposed binding capacity but not the disappearance. By contrast, phenylarsine oxide (inhibitor of endocytosis), N-ethylmaleimide, and phenylmethanesulphonyl fluoride inhibited the receptor loss, suggesting that the loss occurred by proteolysis. The insulin receptor concentration, studied in parallel, remained practically constant in the investigated period in the presence and absence of digitonin. Thus, the hepatic receptor for alpha 2-macroglobulin.protease complexes is regulated independently of other specialized plasma membrane proteins.     

SYSTEMIC INSECTICIDAL ACTION OF NICOTINE AND CERTAIN OTHER ORGANIC BASES

Nicotine and nicotine salts are taken up by the roots of plants from solutions, and when 0.01–0.001 % nicotine is used the plants become toxic to Aphis fabae and to Pieris brassicae larvae and can be shown to contain nicotine. The results with Phaedon cochleariae adults and larvae are less satisfactory. No systemic action is observed when the nicotine is watered on to soil in which plants are growing and no nicotine can be detected in the plants. Apparently the nicotine is decomposed in the soil.
When applied several times to the upper surface of a bean leaf nicotine kills aphids on the underside. There is some evidence that nicotine can be translocated further through the plant following leaf applications, but the toxic action at any distance is very weak in the plants used in the present experiments and can only be produced by frequent applications of rather concentrated nicotine solutions. Leaf absorption and subsequent translocation has not been observed with nicotine salts.
The various organic bases, including some piperidine phosphonites and allied compounds tested, are of very little interest as contact or systemic insecticides against aphids.